Here is the full list of all 21 Rubber Ducky and the Rainbow Gun achievements.
I told you to go right, didn't I. . .?
Be addicted to social media.
Buy all the costumes!
This one's not too hard to find. . .
You're the best! :D
It's a practical paradise, just for you!
Well, it's still there. . . just less dire.
Looks like someone just likes firing the Rainbow Gun. . .
Well, it's sorta' in the level. . .
It's there, it's unique! Just look closely!
Everyone knows it's the best part!
. . . or it would have been, anyway!
Have the game run below 30 Frames Per Second.
Unlock all the levels!
Beat the dev's score on the last level! (You might want to shoot for around 1500)
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.
Place fifty-jillion (100) plants in the bounce house at once.
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. . .