Here is the full list of all 37 Outskirts achievements.
Beat the true last boss without any damage
Beat the true last boss
Finish twelveth level without any damage
Finish eleventh level without any damage
Finish tenth level without any damage
Finish eighth level without any damage
Finish seventh level without any damage
Reach a score of 10'000'000
Finish fourth level without any damage
Finish sixth level without any damage
Finish fifth level without any damage
Use super-combo to increase multiplier and give points
Use super-combo to earn a life or points
Use super-combo to gain a power up
Finish third level without any damage
Finish second level without any damage
Finish sixth hard level
Finish fifth hard level
Finish fourth hard level
Finish third hard level
Finish ninth level without any damage
Finish second hard level
Finish first hard level
Begin Outskirts second lap
Finish sixth level
Finish fifth level
Finish four level
Use super-combo to change every enemies color
Finish first level without any damage
Finish third level
Reach a score of 1'000'000
Finish second level
Use super-combo to refill your bomb
Finish first level
Play Outskirts for the first time
Finish the tutorial
Launch the game