Matt Bird writes all sorts of nonsense, but he dedicates a large chunk of his time to writing game walkthroughs.
The action is picking up in Kingdom Rush, and Silveroak Outpost is under attack from multiple angles. Can you defend it from the forces of darkness?
This stage is another split-path affair. There are two streams of enemies:
The primary set comes from the south. Here you'll encounter waves of the usual fiends, though they'll split up and follow two different paths. Make the most of the first intersection by setting up your strongest towers on its corners, allowing said towers to target your foes before they split. With a few strong towers here you can potentially kill most enemies before they branch off. This spot is also fantastic for any castings of Rain of Fire.
The second wave of fiends, all spiders, comes from the east. Spiders are weak, but they come in great numbers which can overwhelm your soldiers and slip past. An Archer Tower pre-built in the north can handle any trickle in the early waves, but you'll want at least one or two other towers built on this path for later. Artillery is fantastic for mashing most spiders.
Level 5 Strategy
Silveroak Outpost allows you to upgrade your Archer Towers another level partway through the session, and you should take advantage of this fact by building a fair number of them. Though there are some bandits in this stage that will ward off arrow attacks, most of your foes here are best engaged with Archers. Set up several Barracks to keep enemies in place on the southern path, as well.
This level also presents players with the option of fixing up a barracks in the northwest corner of the map to spawn Sylvan Elves. These units are fairly formidable, but the path on which they're set is not vital enough given the cost. You're better off sticking with the standard set of towers, at least on the normal setting.
Hard doesn't change things much, though Artillery for warding off the spiders is near essential if you don't have a ton of upgrades. If you're a regular user of Rain of Fire (highly recommended), save it for the northern convergence of paths where you can do the most damage to groups of enemies.
Silveroak Outpost's Heroic Challenge
The Spiders in this level's Heroic Challenge don't change a whole lot, so Artillery remains your best defence for the west. Your eastern defences should change a bit, though, as there are a lot more heavily-armoured folks, notably the horde of heavy Marauders that show up at the end. A pair of Mage Towers at the spawn point can help whittle down their health significantly so later troops can bring them down more easily. A Barracks in the north that's fully-upgraded is essential to stopping trickles.
Silveroak Outpost's Iron Challenge
Iron Challenge in Silveroak Outpost changes things up significantly. Not only do you have three ready-made Archer Towers at your disposal, your ability to make Barracks is gone. Very bad, this, though the presence of two Sylvan Elf spawning points will even up the score.
Set up Artillery to off the spiders while repairing the barracks and keeping the number of Elves spawned at the maximum on both paths. Do this and beating off the bad guys is not nearly as hard as it looks.