Here is the full list of all 21 UDO achievements.
Explode 3 enemies at once with the "Danger Zone" skill
Summon all companions from the "Necrodrill" skill
Use an enemy to kill another enemy using the bowling skill
Reach exactly zero of fuel amount
Finish the tutorial
Find a secret area
Do not receive any damage from the boss
Do not receive any damage from spikes in the "Buzzing Caves" section
Do not receive any damage from acids in the Bumping Biosphere section
Do not receive any damage from the toxic gas in the Barren Lands section
Do not receive any damage from the giant laser in the Forsaken Labs section
Get to a total of eight life points in a run
Maximize the total deck points
Finish a cave section without jumping
Find the secret deep below
Reach 50 combo count
Get all upgrades from the main CPU
Find all skins
Finish a run without getting new upgrades
Finish a run
Get to a total of 200 fuel points in a run