Here is the full list of all 22 Plunge achievements.
Escape with Warden
Discovered all potions
Unlock Warden
Escape with Mortar
Escape with Crook
Escape with Chant
Escape with Bellow
Unlock Mortar
Escape with Nox
Escape with boy Billie
Spare 200 enemies
Unlock Crook
Unlock Chant
Unlock Nox
Unlock Bellow
Unlock boy Billie
Enter Turbo Slammer 2
Escape with girl Billie
Clear the Voidblocks
Defeat 500 enemies
Clear the Madblocks
Clear the Ironblocks