Here is the full list of all 22 Elliot Quest achievements.
Get the Bad Ending
Find the Potato Man
Defeat the Worm Ancient Boss
Rescue Terry
Obtain all Crystals
Find Rasa's home
Defeat the Colossus Ancient Boss
Find all three Yellow Mushrooms
Find Cloaked from Cloaks and Spells
Collect the Shovel
Find the Forest Maze area's map
Find a special statue
Collect the Golden Shield
Find the Moonman
Get the Good Ending
Get the Neutral Ending
Defeat the Rhino Ancient Boss
Defeat the Bouncing Totem Ancient Boss
Defeat Tema
Get past level 20 at the Colosseum Battle Ground
Unlock New Game Plus
Collect all the hidden paintings