Here is the full list of all 21 Rubber Ducky and the Rainbow Gun achievements.
Buy all the costumes!
Have the game run below 30 Frames Per Second.
Everyone knows it's the best part!
It's there, it's unique! Just look closely!
Place fifty-jillion (100) plants in the bounce house at once.
This one's not too hard to find. . .
Looks like someone just likes firing the Rainbow Gun. . .
It's a practical paradise, just for you!
Well, it's still there. . . just less dire.
You're the best! :D
Well, it's sorta' in the level. . .
I told you to go right, didn't I. . .?
. . . or it would have been, anyway!
Unlock all the levels!
Beat the dev's score on the last level! (You might want to shoot for around 1500)
Be addicted to social media.
Type the 2nd section of the dialog from the 6th level backwards into the cheat code selector! Don't forget to puncuate and capitalize properly!
Convince/bother/bribe the dev until everyone gets this achievement.
Get below 8:00 in speed run mode.
Play with Death Epileptic Pixel mode on. (There's also a game of the same name)
You've defeated the derpy brother and unlocked a message from the developer. . .