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