The big yellow snake boss, take him out.
Miniguns treads and homing missiles. Terminate the Robo Boss.
Check out the big brain on Brain Boss. Take out the brains of the operation.
Just play the game.
Winner winner. Beat the game.
Discover a secret.
Kill a mimic.
Launch an enemy with an explosion.
Use a mystery warp.
Buy all the items at a single shop.
Unlock a perk.
Roll under an enemy projectile to avoid damage.
Clear a room with 3 or more necromancers.