Here is the full list of all 27 HackyZack achievements.
Complete all levels in World 2.
Unlock Fell as a playable character.
Collect all stickers in W2.
Complete all levels in World 1.
Unlock Frog as a playable character.
Collect all stickers in W1.
Complete all levels in World 3.
Complete all levels in World 4.
Complete all levels in World 5.
Complete all levels in World 6.
Unlock Kelly as a playable character.
Unlock Fara as a playable character.
Unlock Shadow as a playable character.
Collect all stickers in W3.
Collect all stickers in W4.
Clear all of W1 target levels.
Clear all of W2 target levels.
Clear all of W3 Target Levels.
Clear all of W4 target levels.
Clear all of W5 target levels.
Clear all of W6 target levels.
100% the game.
Beat all Target level Normal times.
Beat all Target level Dev times.
Collect all stickers in W5.
Collect all stickers in W6.
Unlock Leroy as a Playable Character.