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