Atom Zombie Smasher Strategy Guide: how to beat back the Nuevo Aires Zombie Infestation with your mercenaries
I found this fun little game on Steam (the game distribution platform developed by Valve) called Atom Zombie Smasher. It's such a fun little game, I've been playing it for dozens of hours, and I decided I need to write a strategy guide on it.
The game takes place in the fictional region of "Nuevos Aires", which is being invaded by zombies. You have a variety of offensive and defensive units, and your objective is to rescue as many civilians as possible, and hopefully beat the zombies. There is a bit of research, and your units level up RPG style as they gain experience.
The game has two modes: the "map mode", where you choose to attack individual territories and rid them of zombie menace, and the actual "city mode", where the combat takes place. In a sense, this is reminiscent of XCOM or Starfleet Command, which has separate strategic and tactical layers.
Watch the "trailer" above and you'll get a sense how the game is played... On this 3D overhead city map. Helicopter (yellow icon) swoops in to pluck civilians from the lavender zombie hordes. Snipers (cyan icon) engage zombies from up top. Artillery (orange icon) is reloading for another salvo while shells are raining down from above, and infantry (green icon) is engaging zeds trying to buy more time for the civilians (yellow dots) from the advancing zombie horde (cyan dots).
Because we start on the "meta game" screen, i.e. the map screen, let's explain the elements on there. Then we'll go over the individual elements on the "city screen" playing field.
Map Screen / Meta Game
The overall objective of Atom Zombie Smashers is to score victory points, and reach the goal (set at beginning of game) of 1000, 6000, or 20000 (or custom) amount of victory points before the zombies do.
You score victory points by killing zombies, winning missions, rescuing civilians, and capturing territories. Territories captured (by killing every zombie within the time limit) generates victory points every "turn" on the map screen.
Zombies score victory points by killing civilians, make you lose missions, and infecting more territories. However, they cannot spread into "won" or "captured" territories. They can, however, appear randomly into 'disputed' (grey) territories, and if you get "level 4" infestations, that will spread into adjacent territories as well.
The elements, starting from upper left corner, going counter-clockwise:
The options menu -- allows you concede, restart, save game, etc.
The numbers -- shows you what level of infestation there is in that territory. Level 4 infestation can spread to adjacent territories, so should be attacked ASAP. Furthermore, every infested territory gets the zeds some "victory points", and the higher the infestation level, the more points they get.
Captured territory (tan color) -- every territory where you won by killing every last zed before the timer expired counts as captured, and generates "victory points" for you. It is assumed that defenses worked and civilian life have resumed.
The current game time -- just for flavor
Won territory (black color) -- territory where you evacuated sufficient civilians to count as "victory", but did not kill every last zed, is assumed to have been nuked and nothing alive or dead remained. As such it does not generate victory points for you, but zombies cannot invade it either (no bodies to infect).
Special event -- every month a different event occurs and a modifier is applied. This month, the days are slightly shorter, giving you less time to kill zeds and accomplish your mission.
Your HQ -- is your home province.
Mercenaries on away mission -- these mercenary units are not available for your current mission.
Mercenaries available -- these mercenaries will be deployed for your next mission. Choose your mission wisely based on what units are available!
Scientists -- scientists you rescued can be spent to upgrade various aspects, such as better cannon (firing several shots when each salvo is fired), faster orbital cannon recharge, mercenaries get faster experience, growth, and so on.
Strategy on the Map Screen / Meta Game
Choosing which mission to tackle is extremely important, as it will affect the rest of your game, esp. in the long games.
You will always have a rescue heli, but the availability of the rest of the units will depend on random factors. For organization, I've classified the units as "offensive" and "defensive" units.
- zed bait
Don't Tackle Something You Can't Handle
If you only have defensive units, or merely ONE offensive unit, you cannot hope to hold back the tide of zeds, thus, your objective is to delay the zeds for civilians to escape. As such, you should only attempt level 1 missions. When your mercenaries are experienced, then you may be able to handle level 2 or level 3 missions. But do NOT tackle level 3 and 4 missions without some VERY good artillery and level 5 (or higher) mercenaries.
There is an exception: if you have the "elephant bird test" mission, where you have just one "elephant bird gun", that gun is so good you can easily handle a level 4 infestation (assuming you didn't get the bad luck of having been surrounded by gas line buildings).
Go for Territories that Cuts up the Map and surround the zombies
Territories that can cut the map up into sections are vital to limit the zombie infestation. Zombies cannot re-invade territories they have been beaten from (both tan and black territories) under normal conditions and thus if you can can surround the infestation they cannot spread to contested territories except through random infections, and that is limited to maybe 3 per month in late game (just 1 per month at start). If you let a level 4 infestation untouched without attempting to contain them they will EACH add 2-3 infected territories per month, PLUS the random infections (up to 3), and then you'll lose the campaign as the zeds generate far more victory points per month than you when they add like 5-10 territories per month and you add like ONE a month.
Let me illustrate this with the same picture, albeit labelled a little differently:
Look at the map and note the territories labelled A, B, C, and D.
If you invade / evacuate territory A, a level 2 infestation, you can block off that level 4 infestation in the northeast entirely. It cannot infect any more territory from there.
If you invade territory B, you can block off the level 4 infestation from spread southwest, forcing it to spread north / northeast.
If you invade territory C and D, you don't really gain any control over the map.
So between A and B, which one should you choose? The answer is A. Why? Because B, while tempting, can actually wait one more turn. The territory just to the east of B (between C and level 1 in the south) is still a chokepoint. You can hit it a little later and still contain the infection in that direction.
You have to do this evaluation for every potential target territory every turn, based on your available units.
How to use llama Bombs Effectively
Llama bombs are nukes that will zap the zombies in MULTIPLE territories (up to 4 at a time), if you have a good concentration of them. You are given a few of them during the campaign for free. Use them wisely. Remember I asked you to "cut up the map" into manageable chunks? This is why: so you can zap them with llama bombs.
Look for concentration of infected territories, then move the cursor at the borders where they come together, so you can zap as many territories as possible with just ONE bomb.
There is an research upgrade that gives you an extra bomb (default is 2) if you spend the points for them.
Let us look at a visual example. Using the same map as before, I have highlighted several possible aim points for the llama bombs.
Let us look at the five different Llama bomb targets I've pinpointed.
Target A - potential damage is 9 (4+4+1) (renders B superfluous)
Target B - potential damage is 10 (4+4+2) (renders A superfluous)
Target C - potential damage is 5 (2+3) (renders D superfluous)
Target D - potential damage is 7 (4+3) (renders C superfluous)
Target E - potential damage is 6 (2+2+2)
If you only have 2 bombs, you should pick target B and target D. If you have a third bomb, hit target E as well.That would leave you with the minimum amount of infestation on the map.
The Victory Bar and Fixed Events
Victory bar, which only appears at certain times on the map screen, shows you the progress of each side, how many points, and so on. However, there are certain "dots" on the bar itself. Those are fixed events. Some of the special events include
Mega Zeds -- giant zeds that brings down buildings, and can only be killed by artillery
Super Blimp -- you can now take even more units into battle
Unlocking Catbird Cannon -- a space cannon you can call upon in battle, based on civilians rescued and zeds destroyed
Llama bomb tests -- free llama bombs to take out a few zed territories.
and so on.
Move the mouse over the dots to see what are the events.
Plan for these events and don't get surprised by them.
Research / Scientists
As you rescue scientists, you can "spend" them to buy items in the research center, which will give you various enhanced capabilities. (NOTE: Not all research is available at all times, some are only unlocked at certain victory point levels)
The research items are
- Increase helo carrying capacity
- Increase llama bomb capacity
- Improve artillery (shells per salvo)
- Increase XP gained per kill
- Improve elephant bird special artillery (shells per salvo)
- Improve space CATBIRD cannon unlock rate
- Improve explosive damage to Mega Zeds
- Scientists run faster
Increase helo carrying capacity
Increase helo carrying capacity by 5 (default is 30)
Increase llama bomb capacity
You get one MORE llama bomb per salvo. (Default is 2, when available)
Improve artillery (shells per salvo)
More shells per salvo means you can shoot several shots before you reload!
Increase XP gained per kill
Gets extra XP per kill, works for ALL mercenaries.
Usefulness: A, every little bit helps make your mercs better, and 10% really adds up!
Improve elephant bird special artillery (shells per salvo)
Lets Elephant Bird artillery fire even MORE often
Usefulness: D, elephant bird is already strong enough!
Improve space CATBIRD cannon unlock rate
Unlock the CATBIRD cannon faster
Usefulness: C, CATBIRD cannon is only useful in cleaning out large amounts of zed infestation and mega zeds, as it flattens an area completely.
Improve explosive damage to Mega Zeds
Explosives like artillery, dynamite, mines, etc. do 50% more damage to mega zeds.
Usefulness: B, only buy this when you started seeing Mega Zeds.
Scientists run faster
Scientists now runs faster than civilians toward rescue helo.
Usefulness: D, you could just LAND next to a scientist.
City Screen / Tactical Combat
Zed infestation enter a city two ways: either they are already in the city (only happens very rarely), or they are about to enter.
If they are already in the city, then you just have to do what you can, as you are likely to lose the mission, unless you are VERY lucky and have SEVERAL infantry units ready to spread out and control the infestation and carve out an "safe area" for your helo landing zone.
In the invasion scenario, where the zeds are about to enter the city via known routes, there are two types: evacuation, and eradication (attack). Each entrance is denoted by one skull head on the city map. Level 1 infection has 3, level 2 has 6, and so on.In evacuation, your objective is to rescue as many civilians as possible. You need to rescue at least a certain number to be considered "victorious" (that's in the upper right corner), else you have lost the mission and you can retry (unless you have permadeath turned on). As long as there are still civilians alive, the mission goes on, even if you no longer have daylight.
In eradication, there are no civilians in the city, so your objective is to simply kill as many zeds as fast as you can, preferably before darkness falls. Generally eradication missions are level 4 infestations, which means zeds are coming through in streams from all sides, usually 3 entrances per side.
Let us look at one guy's attempt to control a level 2 infection, with just infantry, barricade, and cannon.
That is actually NOT the optimal placement for the 3 barricades available. As is, the two groups (right and bottom) will converge and the infantry can't kill the zeds fast enough.
Instead, the infantry should swap places with the rightmost barricade. Why? One infantry is often enough to kill all the zeds coming out of a single entrance (esp if that unit has 60% or higher accuracy). By forcing all the other zeds to walk over you spread them out and defeat them in detail (one group at a time).
Note how this player attempted to block the zombie flow by adding barricades to force the zombies into that single chokepoint, even if they entered the city at six different places. All firepower he had are concentrated at that spot to slow down the zeds and buy more time for the civilians to evacuate.
(That is NOT the optimal placement, see sidebar to the right on why that is so.)
When the skulls disappear, that's all the zombies that are coming through (unless you can't finish the mission during daylight and more zombies invade at night).
Offensive Mercenary Units
Mercenary Units can be classified generally as offensive, or defensive.
Here is a roundup of offensive units:
- rescue helo
Infantry is probably the most versatile of all units. It can be moved, or left in place to defend chokepoints. When upgraded to 80% to 90% damage it will do a decent job at killing zeds. Unfortunately, you never seem to have enough of them, and because they kill one zed at a time, they can't kill zeds fast enough.
Infantry CAN be killed if something nearby explodes, be it mines, artillery, explosives, or an exploding building. They cannot be killed by zeds.
Infantry should be placed near entrance points to whittle down the enemies. When the horde is too thick, they can be pulled back and artillery dropped in their wake. They are also useful in helping to wipe out the few survivors so you can claim the "total victory".
Infantry level up by making kills. The more kills, the more exp they get, and the more they level up. Picking upgrade to improve their firepower would make them level up even faster.
When upgrading infantry, upgrade their lethality (i.e. accuracy) is the most important. When you get it to 80% or 90% you can work on their speed a little bit.
Sniper team is immobile. Once you put them on top of a building, they are STUCK there. And if the building comes down, they die. On the other hand, they can engage all the way across the map, even if the shot appears to be blocked by buildings. Just beware that on some mods with larger maps, or if you put the team in a corner, their fire may NOT reach COMPLETELY across the map.
The trick to use sniper teams is put them AS FAR AWAY from the enemy as possible. Either along a map's edge, or in a corner.
Once sniper team is placed, you also need to designate where they should aim at. Where you place that "aimpoint" determines what enemies they will engage. When you select the unit, you can see their engagement "cone" (white/cyan highlighted area). If there are multiple targets within that zone, they hit the one closest to the aimpoint, not the one closet to THEM. Thus, you should set the aimpoint closer in then further out else your snipers may ignore closer targets in favor of ones further out.
Sniper team CAN be destroyed if the building they're on is destroyed through any means, would include explosives, mines, artillery, exploding gas line building, or a megazed walking into it.
Sniper team level up by number kills, so improving their firepower (minimize refire delay) gives them more XP as well.
Snipers should get their upgrade in refire delay ASAP, as this essentially increases their firepower. Repositioning delay can be lived with and worked on later.
Artillery is an area weapon: a shell comes down somewhere within the circle, and the explosion kills everything in that area. Artillery must be placed on top of a building. In general, you don't want to be on top of a gas line building (in red) or anywhere near it because if the building is destroyed, the unit is destroyed as well.
Artillery has a "danger close" radius where it cannot shoot if enemy is too close. Thus, artillery should be deployed as far from the zeds as possible. That distance does NOT affect time to impact. Otherwise, you may need some other units, such as sniper and infantry, to clean out the ones that got too close.
Artillery CAN be destroyed if the building they're on is destroyed through explosives, mines, exploding gas line building, other artillery, or even a megazed walking into the building.
Artillery is best employed upon a concentrated horde of zeds, such as them being bunched up right at their entrances. The problem is their somewhat imprecise nature means they destroy the buildings near where they are, and that can mess up your path planning.
There are two delays involved with artillery: time to impact, and reload delay. Time to impact basically is how long the delay is from the time you gave the order to fire, and when the shot actually hits your target. Obviously, the longer the delay, the more you need to "lead" the target. Most zeds don't move fast enough to outrun a 5-second delay, though at 7-second delay it gets hard to hit them precisely. (NOTE: Mega Zeds move faster)
The reload delay improvements increases your firepower by squeezing out more shots in the same amount of time. That helps it to level up by killing more zeds and gain more experience.
You can further increase the firepower by buying increased magazine size with scientists. When your artillery levels up it also fires more shots at once.
Rescue helo technically is not a weapon as it does not kill zeds, but it is mobile. I'll lump it under offensive for now.
Rescue helo is the way civilians leave the infected territories, and why you're fighting the war against the zeds. Designate the landing zone. The helo will sound a horn and all civilians within a certain radius will hear it and attempt to run toward it (may not always be possible) due to barricades and so on.
You can designate new landing zone before the helo actually lands. Once it lands, it is on a timer. When that timer ticks to zero, or when it is full, it will take off. You can also tell it to take up early with that "rise up" button next to the chopper if there's no reason for it to wait.
Rescue helo gain experience (and level up) by rescuing civilians and scientists.
Rescue helo's use is obvious, but what is NOT obvious is you should move the landing spot slightly after each use, esp. if the zeds are coming to one side. Through the nature of the helo "summoning" all the civilians within the radius of that broadcast, you can "pull" the civilians away from the zeds.
Helo can be improved two ways: faster loading, or faster flight (into and out of the battle zone). In general, faster flight is more useful than faster loading, at least until you get to point of diminishing returns. Spend at least the first 2-3 upgrades on faster flight.
You can also spend scientists to buy slightly larger capacity so more civilians can be evacuated at once. Default is 30, and upgrades can be bought to increase cabin size to 35 or even 40.
NOTE: Helo cannot be destroyed, even by exploding buildings and artillery. On the other hand, all that stuff kill civilians as well as zeds.
Defensive Mercenary Units
The defensive mercenary units are:
- zed bait
Barricade is arguable most versatile defensive unit. While it kills no zeds by itself, it helps almost everything ELSE kill zeds.
Barricades have special placement rules, and must be placed before the battle. Basically, you must leave a path through the city, so any entrance into the city can actually LEAVE the city, though it doesn't say how many twists and turns it required. Thus, with sufficient barricades, it is possible to contain the zed infestation and force them to bunch up into a single path, making them vulnerable to your other weapons.
See the previous picture for an illustration on how barricades are used to create a chokepoint which is then defended.
Zed bait is a beacon that attracts nearby zeds. It is best used as a delaying tactic, or to concentrate zed horde to make them more vulnerable to your other weapons, such as artillery and space cannons.
Zed Bait is of limited duration (starts at 7-8 seconds, but can be improved). The effectiveness radius can also be improved in order to attract more zeds, and reload time can be decreased.
Zed bait in general is used two ways:
a) to buy time by forcing the zeds to take a more indirect route. Every X seconds it has to spend walking toward the beacon is X more seconds you get to keep killing them with the weaker units like sniper and infantry, and more time for the helo to evacuate more civilians.
b) to pull them to a specific spot where they are then toasted by artillery or space cannons, or across mines and explosives.
Do NOT place zed bait upon start of mission, because there are no zeds on the map yet! Know where you need to put one when the time comes, but not yet!
Dynamite is a basically explosive with manual detonator. When given the command, within a second or two each one will blow up, hopefully taking out a large chunk of zeds and not killing civilians.
NOTE: Dynamite detonation is not simultaneous, but in quick succession, with the first one placed detonating first, and so on in order.
When used with barricades, put these along the single path, spread out, so you can take out a large chunk of zeds all at once.
If you don't have barricades, then put them directly in the path of the entrances, albeit slightly back (about 3 grids), so you take out a whole group of them at once.
Beware, dynamite will often bring down buildings. Don't accidentally blow up your own units by dropping their building or building(s) near them, esp. gas line buildings (dark red).
Gas line buildings can be detonated by dynamite as well.
Mines / Minefield
Mine unit is difficult to use. The zeds don't move THAT fast to outrun mines, but the damage radius is small enough so that you need to stack them (2-3 all in the path of the horde) to do decent amount of damage, and you never seem to have enough. it needs to be combined with barricades, dynamite, and so on for a defensive perimeter.
Another possibility is to "stack" them in front of the entrance. If you put two or three of them (i.e. stack them) with a gap between them, you can often destroy one group of zeds, depending on the amount of zeds coming through. You can put infantry and other units on the other entrances.
If you plan to detonate a few gas line buildings, a mine is a great way to do it, just put it on a spot you know the zeds will walk by, and next to such a building, and watch the fireworks. However, such a building that is next to a zombie infested street isn't always available. In that case, a dynamite MAY be more appropriate (if available).
Ten Tips for Beginners
- Learn to hit the SPACE BAR, which toggles between two speeds... fast, and slow. On my PC, I set fast at 70%, and slow at 10% (use + / - to change speeds). That, for me, is ideal. When things are too exciting, toggle to slow (or even turn off the speed completely and make it a "pause" button). When waiting for reload, flip it to fast.
- Turn on "Casual" option when first starting. If you don't, the game may be too hard for first-timers. Casual mode turns off "mega zeds" and makes all zombies slower and daytime longer.
- Learn how to place each unit optimally. Some units need to stay away from the enemies, while others need to get close.
- Don't panic. Unless you got "Permadeath" option turned on, you can always hit F9 to restart the mission. Even if you fail the mission, you can just hit restart to try again.
- Artillery is king of battlefield for a reason, even this fictional one. Artillery will kill zeds much easier than all other units. because it kill them in DROVES.
- Infantry can be moved to chase down that last zed, or to block chokepoints, but it usually cannot stop zeds alone, at least early on, because it kills only one zed at a time. Back them up with other units.
- Use barricades to force zeds into as few chokepoints as possible, and pound them with everything you got.
- Choose the mission that you *can* handle and do the most good. If you just pick a mission at random you'll probably lose unless you're in "casual" mode.
- Rescuing scientists is important... You need them to unlock research stuff to make the game easier.
- Luck is a fickle lady: things can turn against you. There is no shame to concede a mission or two when things are impossible.
Five Tips for Advanced Players
- Your primary objective is to get the civilians (and scientists) away from the zeds. Killing the zeds is simply the means to that objective. Don't lose sight of the real goal.
- NOT all civilians can be saved, unless you are extremely lucky or have very powerful units (which are also a lot of luck). So don't fret it if you have to sacrifice a few
- AZS relies on "forward defense", i.e. block the entrances (except the few missions where a few zeds are already in the city.) So any tactic is done with that in mind: defend those entrances and get the civilians AWAY from there to be evacuated
- Try not to "mix" different weapons on the same zed entrance. Exploding dynamite, mines, or artillery don't mix with infantry. Infantry's range is limited any way and needs to stay away from the explosions.
- Keep an eye on the "clock". You don't want to be surrounded by bazillion zeds if you can help it. As long as you kill all the "original" zeds, you get credit for full extermination. In fact, I've seen this happen even after the "new" zeds appeared on the map.
Additional Game Options
When you start a new campaign, you can choose among the different campaign victory options:
- 2000 points
- 6000 points
- 20000 points
- custom setting (enter a number)
The more points, needed to win, the longer the game (and more likely the zombies will win).
There are a few more options and how they affect the game:
Fully Stocked (makes game easier) -- normal game starts with just the rescue helo. Additional units must be unlocked by playing through a few missions. Fully stocked gives you all units at once (though some of the units may still be unavailable)
Party Wagon (makes game easier) -- lets you carry one extra merc unit, makes a bit difference early on
Llama Pile (makes game easier) -- instead of only receiving llama bombs via victory point milestones, you can spend scientists to buy llama bombs. Standard price is 20 scientists for 2 bombs. (Number of bombs can be increased by buying the llama research)
Combatant (makes game easier) -- on some missions you may end up with ALL defensive units, and that can be extremely frustrating. This makes sure you have at least one combatant, namely artillery, sniper, or infantry.
Casual (makes game easier) -- actually, this makes the game extremely easy, almost impossible to lose once you learn the mechanics (and read this guide)
Hardcore (makes game harder) -- this makes the game quite tough. Zeds are faster, daylight time is shorter, and all that.
Triplets (makes game easier) -- normally the game will not let you carry more than one of the same type of unit (i.e. you won't get two infantry). This will override that restriction.
Chooser (makes game easier) -- normally the game picks which units are available for the next mission. This lets you actually choose among the units available.
Permadeath (makes game harder) -- Normally you can always restart the mission if you do really badly. Permadeath means if you lose, you must concede.
Alt. Spawning (makes game A LOT harder) -- instead of entering the city via known entrances, the zeds are ALREADY IN THE CITY. If you can win missions consistently like this, you are VERY good.
No Quarter (makes game A LOT harder) -- normally the "won" and "captured" territories cannot be re-invaded by zeds, and you can use that to control their spread. This turns off that restriction... Zeds can invade ANY territory, even captured and won ones.
Achievements in this Game
Following are the list of achievements (visible on Steam) for Atom Zombie Smasher:
Share and Share Alike -- Download a mod.
Bookworm -- Unlock all the vignettes.
Zed Industrial Complex -- Complete the campaign.
Long Arm -- Accrue 10,000 sniper kills.
Big Dipper -- Rescue 40 or more people in one helicopter pickup.
The Operators -- Accrue 10,000 infantry kills.
The Big Stick -- Accrue 10,000 artillery kills.
Tactical Camelid -- Cleanse four Zed territories with one Llama Bomb.
Multiplicity -- Complete a campaign with the Triplets modifier.
Long November -- Complete a 20,000 point campaign.
Llamas on Demand -- Purchase a Llama Bomb.
Champion of the People -- Rescue everyone in a mission.
Choplifter -- Rescue 100 people in a mission.
Rescue Raider -- Rescue 200 people in a mission.
Maximum Overrescue -- Rescue 300 people in a mission.
Giant's Drink -- Destroy a Mega Zed.
Night Owl -- Survive the night.
The Big Leagues -- Complete a level-3 outbreak mission.
The Worm has Turned -- Complete a level-4 outbreak mission.
Spring Cleaning -- Destroy all Zed in a mission.
Snipe Hunt -- Use snipers to destroy 100 Zed in a mission.
Street Sweeper -- Get 100 infantry kills in a mission.
Bombardier -- Destroy 50 Zed in one artillery strike.
Powder Keg -- Destroy 50 Zed in one dynamite explosion.
Watch Your Step -- Destroy 50 Zed in one landmine explosion.
From Above -- Get 100 artillery kills in a mission.
Lit Fuse -- Get 100 dynamite kills in a mission.
Hit Somebody -- Get 100 landmine kills in a mission.
Ten Thousand Hours -- Have a merc reach Level 5 veterancy.
Auteur Theory -- Create a new mod.
Remote Control -- Accrue 10,000 landmine kills.
Wrecking Crew -- Accrue 10,000 dynamite kills.
Llama-rama -- Launch 500 Llama Bombs.
International Killing Machine -- Complete a campaign with the Hardcore and Permadeath modifier.
The Gold Standard -- Accrue 500 gold medals.
How Fast They Are -- Complete a mission under 30 seconds.
The Lucky Ones -- Rescue 100,000 people.
Hypothesis Now -- Rescue 10,000 scientists.
They Live -- Complete a campaign with the Alt. Spawning modifier.
The Diplomats -- Complete a mission with 3 players.
Dog Days -- Rescue at least 100 people in July.
Mods and what they do
AZS also supports mods. Basically, a mod is a "tweaked" game where you play under different rules, such as more/less zeds, more/less victory points, faster upgrades, no/extra space cannon, and so on and so forth.
You can access the "mods" through the button on the main menu. At first, you have zero mods. You will have to download some. Click on the "online" button and you'll see a list of all the mods available. Most of them are junk, so you will want to sort the results by the number of downloads and higher positive ratings.
The mods make the game easier or harder, or modifies how the game works fundamentally. Some make things more realistic by making choppers taking a lot longer to evac civilians, or a lesser "summon" radius, others tweak the artillery and/or space cannon (some disable them altogether). Some emphasize infantry, sniper, and artillery, while shy away from the defensive units. Many of them have some of the optional difficulty factors already enabled.
Download a few and see how you like them. You can only have ONE mod active at a time.