There are a total of 25 minigames in It Takes Two that you must find in order for this to unlock. They are scattered throughout the game, and show up in chapter select at any time. They save right away, and you can back out if you are mopping up. They are as follows:
The Shed: The Depths:
0:27 - Minigame: Whack-A-Cody
0:52 - Minigame: Flip the Switch
The Tree: Captured:
1:30 - Fried Friendship Achievement/Trophy
2:09 - Minigame: Tug of War
The Tree Deeply Rooted:
2:38 - Struck A Pose Achievement/Trophy
3:24 - Minigame: Plunger Dunger
Rose’s Room: Pillow Fort:
3:51 - Minigame: Tank Brothers
4:13 - Plastic Prison Break Achievement/Trophy
Rose’s Room: Spaced Out
5:17 - Minigame: Space Walk
6:04 - Minigame: Laser Tennis
6:45 - Faraway Frequencies Achievement/Trophy
8:00 - Look at Him Go Achievement/Trophy
Rose’s Room: Hopscotch:
8:40 - A Daring Devil Achievement/Trophy
9:24 - Minigame: Rodeo
9:46 - Minigame: Feed the Reptile!
10:14 - Break the Bank Achievement/Trophy
10:51 - Minigame: Batting Team
Rose Room: Dino Land:
11:08 - Snackosaurus Achievement/Trophy
Rose’s Room: Once Upon a Time:
11:43 - Minigame: Birdstar
12:11 - On the Rails Achievement/Trophy
12:51 - Realize Your Art Achievement/Trophy
Cuckoo Clock: Gates of Time:
13:39 - Minigame: Bomb Run
14:19 - Platforming Prodigy Achievement/Trophy
15:50 - Minigame: Horse Derby
16:17 - Force Triangulated Achievement/Trophy
Snow Globe: Winter Village
17:25 - Lost and Found Achievement/Trophy
18:40 - Mood Swing Achievement/Trophy
19:30 - Minigame: Snow Warfare
20:12 - Minigame: Shuffle Board
21:09 - Minigame: Icicle Throwing
Snow Globe: Beneath the Ice:
22:04 - Something Fishy Achievement/Trophy
22:50 - Terror of the Seven Seas Achievement/Trophy
23:32 - Minigame: Ice Race
Garden: Green Fingers:
24:16 - Bug Sized Relaxation Achievement/Trophy
Garden: Weed Whacking:
24:53 - Minigame: Garden Swings
25:22 - Minigame: Larva Basket
Garden: Frog Pond:
25:53 - Minigame: Snail Race
The Attic: Setting the Stage
26:20 - Minigame: Slot Cars
26:45 - Minigame: Chess
27:19 - Minigame: Musical Chairs
The Attic: Symphony
28:00 - Minigame: Volleyball
28:22 - Meditation Maestro Achievement/Trophy
The Attic: Setting the Stage
28:52 - Minigame: Track Runner