Disney Infinity

This requires online play and can be done with two players each with an extra controller. Both players must have a gold account and can sign in as a guest on controller two.

You must add each other as friends on LIVE to be able to play together.

Simply start a toy box game and invite your friend. Join in with both secondary controllers and the achievement will pop.

While you're at it, quickly get the Acrobat achievement, too:

For this achievement, you just need to play a 4-Player game. You will only need yourself and a partner to do this achievement, but you will both need 2 controllers, 1 Portal each and 2 characters you can place onto the Portals. You should have 3 that comes with the game (Sully, Mr. Incredible & Jack Sparrow). It doesn't matter if you have 2 of the same and import them twice into the game as that will count.

You may likely have to send a Friend Request to each other on the console, however it might be possible that this can be avoided.

First you will both need to complete the Introduction part of the game. This will take you 5 - 10 minutes to complete. You can then return to the Main Menu from this point.

From here you will need to go into "Toy Boxes" and then choose "Pre-Built Toy Boxes". Select "Empty Toy Box" and let the game load.
Place your first character onto the Portal via the left side to spawn them in, then use your to invite your partner into the game. When your both in the game, simply activate your 2nd controller by pressing and choose to sign in a "Guest". Once that's signed in, place your 2nd character on the right part of the Portal, then press to bring them in. Once you both have brought in 2nd characters each giving 4-Players, the achievement will then unlock.

You may also want to go for this achievement a the same time, since this is the only other Online related achievement in the game. The rest of the achievements can be done offline...