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