Here is the full list of all 26 Outcore: Desktop Adventure achievements.
Completed all of the stages in the idle game
Passed the lake fairy's test
Defeated Hartstronk after talking with the time-wasting heart
Opened the mastermind door before receiving its password
Witnessed a memory that didn't happen. Probably?
Murdered a Lumi
Reached the top of the high striker mini-game
Played every icon mini game on the desktop
Defeated the mastermind through the LOVE route
Defeated the mastermind through the HATE route
Defeated the mastermind through the DEMON route
Defeated Captain Tutorial from the first phase without losing any lives
Defeated Booty The Bootleg from the first phase without losing any lives
Defeated the mastermind from the first phase without losing any lives, via the HATE route
Allow Lumi to achieve her dream of becoming a dead web browser
Proved a point by taking an unnecessary self imposed challenge of touching some text during a race
Found the immersion breaking meta menu