Matt Bird writes all sorts of nonsense, but he dedicates a large chunk of his time to writing game walkthroughs.
Every Pokémon generation has its own unique quality, and in Generation VI that is most definitely the Mega Stone. Capable of temporarily evolving some powerful Pokémon into some even more powerful Pokémon, Mega Stones can radically expand your options as a Pokémon trainer. Below are the locations of all of the Mega Stones in the game.
These Mega Stones are given to you either as part of the storyline or, at the very least, are available early on. All of them are usable by starter Pokémon.
- Blazikenite: The first Mega Stone you can get in the game, Blazikenite is only available by downloading the Torchic that comes with Pokémon X and Y. Select Mystery Gift on the main menu, then Receive Gift, then Via Internet. Speak to a woman by the desk at the next Pokémon Center you visit with an empty spot in your partty to receive the Torchic. It has Blazikenite attached.
- Venusaurite, Blastoisite, Charizardite X and Y: There are two ways to get these stones. The first is to select the respective starter Pokémon when given the choice by Professor Sycamore in Lumiose City. He'll also give you their Mega Stone. To get the other two, check out the Stone Emporium on Vernal Avenue, still in Lumiose City. An old man in the back will sell you the other two stones for $100,000 apiece. Note that the Charizardite you receive depends on your version of the game.
These Mega Stones are given to you over the course of the game, either as part of the storyline or by speaking to various NPCs. Unless otherwise noted, you do not have to beat the game to collect these Mega Stones.
- Abomasite: In the rear of Frost Cavern, you'll have to fight off a few Team Flare cronies to protect an Abomasnow. Speak to the Abomasnow after getting rid of Team Flare and it will give you Abomasite.
- Absolite: After reaching Kiloude City upon beating the game, battle at least once or twice in the Battle Maison. Then check out the park in the north. Your neighbour is waiting here, and he/she wants to fight. Beat him/her to receive Absolite. This also unlocks a meeting with Sycamore in Anistar City that's necessary to collect most of the post-game Mega Stones.
- Aerodactylite: After running through Glittering Cave and 'saving' the researcher, revisit the Fossil Lab in Ambrette Town. Speak to one of his fellow researcers on the right side of the lab to receive Aerodactylite. (It's also worth mentioning that you can get Old Ambers, the fossils needed to spawn an Aerodactyl, by Rock Smashing boulders in Glittering Cave.)
- Ampharosite: Travel to Azure Bay, north of Route 12. Upon entering the Bay you'll see an island almost straight ahead, occupied by a trainer and an old man. The old man will hand over the Ampharosite.
- Gardevoirite: After beating the game, revisit the cafe in Lumiose City where you first met Diantha, the (now former) Champion. It's down the street from the Pokémon Lab, to your left when you leave the Lab. Diantha is inside, and she'll trade you a Ralts for any Pokémon you choose to give her. Gardevoirite is attached to the Ralts.
- Gengarite: Have a look in the northwest of Lavarre City for a Hex Maniac. Speak to her and she'll hand over the Mega Stone.
- Lucarionite: You'll have to face Korrine, the Gym Leader of Shalour City, in a one-on-one Lucario fight in the Tower of Mastery. After the battle, she'll offer to give you the Lucario you used. Accept the gift (why wouldn't you?) and the Lucario will have Lucarionite attached.
- Mewtwonite X and Y: After completing the game, revisit Pokémon Village via Route 20. The cave in the north that was previously blocked (and which you'll need Surf to access) will now be open. Inside is a Mewtwo. Catch it and you'll receive Mewtwonite X or Mewtwonite Y, depending on your version of the game.
The remaining Mega Stones in the game are hidden throughout Kalos, appearing on the map as shining, purple tiles. There are two conditions that must be met before you'll find these Stones.
First, you have to upgrade your Mega Ring. After beating the game, visit Kiloude City and participate in a few battles in the Battle Maison. Afterward, check the park in the north of the city to find your neighbour. Beat them in a battle and they'll mention that Sycamore wants to meet you in Anistar City. Visit the Anistar Sundial and Sycamore will upgrade the Mega Ring. You can thereafter find hidden stones.
Second, you have to visit the areas listed below at a specific time - namely, between 8 and 9 PM. Visit at any other time and the Mega Stone will not appear. It's also worth noting that Mega Stones don't always seem to immediately appear; if a Mega Stone isn't showing up, go off-screen and come back. This is especially true if you save in the area where the Stone appears, change the time on your 3DS, and then return.
- Aggronite/Tyranitarite: Make a return to the Cyllage City Gym and climb the wall. On the second level of the wall to your right, at a dead end, is a Mega Stone. Pokémon X users get Tyranitarite; Pokémon Y players will find Aggronite.
- Alakazite: Revisit Reflecting Cave from the Shalour City side and descend into the basement. In the north of this area is a hidden room leading back south. Down here you'll find a big patch of light. The Alakazite is sitting in the middle.
- Banettite: There's a patch of Surfable water near the eastern side of Route 22 which leads to a waterfall. Descend to the bottom and land on the patch of heavily-flowered turf to your right. Through a darkened hole in the rock is the Chamber of Emptiness. The Banettite is in here.
- Garchompite: Walk along Victory Road until you reach the first large outside area (not the bridge, the next one with the ruins). To the left of the path where you emerge from the cave is a wall to Rock Smash. Beyond is a small tower. The Garchompite appears at the base of the tower.
- Gyaradosite: Have a look in the southern half of Couriway Town for the local Hotel. To the right of the hotel is a series of small waterfalls. The Gyaradosite is sitting at the base of one of these waterfalls. (And no, you don't need the HM move to get it.)
- Heracronite/Pinsirite: North of Aquacorde Town and Route 2 you'll find Santalune Forest, an early location in the game. Come back here via the Route 2 entrance and search through the grass just north of the entrance, behind the tree that splits the path. You'll find Pinsirite in Pokémon X and Heracronite in Pokémon Y.
- Houndoomite/Manectricite: The west side of Dendemille Town splits into two paths: north takes you to Route 15, south to Route 16. Head onto Route 16 and, shortly after entering, you'll see skaters patrolling to the south around a rock formation. Against the south end of the formation is the Mega Stone. You'll find Manectrite in Pokémon X and Houndoomite in Pokémon Y.
- Kangaskhanite: Enter Glittering Cave, at the east end of Route 9. Watch for the first turn to your right when you enter the cave. The Kangaskhanite is at the end of the dead end.
- Mawilite: Visit Camphrier Town and check out Shabboneau Castle in the north. The Mawilite is sitting on the second floor of the castle.
- Medicham: Hop to Laverre City. Beside the bridge through town is a well. The Mega Stone is in front of the well.
- Scizorite: Remember that Abomasnow that gave you Abomasite earlier? Revisit it at the rear of Frost Cavern. Hidden behind it is Scizorite.
The Guy on August 12, 2019:
How do you get the Zoroark mega stone?
Lennon on November 20, 2013:
*Houndoominite more precisely.
Wobble on November 01, 2013:
"To get the other two, check out the Stone Emporium on Vernal Avenue, still in Lumiose City. An old man in the back will sell you the other two stones for $100,000 apiece. Note that the Charizardite you receive depends on your version of the game."
Actually, it depends on how much style you have. I had the guy offer me Blastoisnite for 300,000, which is different. The more style you have = the less you have to pay.