Here is the full list of all 14 198X achievements.
Complete The Runaway
Complete Out of the Void
Complete Beating Heart
Complete Shadowplay
Complete Kill Screen
Complete 198X
Complete Shadowplay without taking damage
Collect all power-ups in Shadowplay
Complete Beating Heart without dying or using pick-ups
Destroy every enemy in Out of the Void without losing a life
Complete The Runaway without a single collision
Complete the Kill Screen maze using only super effective attacks
Reach level MAX in Kill Screen
Watch the end credits all the way through - thank you backers!