Have 6 Improvements at one time.

Play a multiplayer game

Block 5 projectiles in a row using your sword

Complete a level without dying

Defeat the Keymaster

Kill a Splitter before it manages to split itself

Kill 3 enemies with a single use of Tempest

Force enemies to kill 4 of their allies using Overlord

Defeat Hel

Kill an enemy with a projectile reflected by Tempest

Kill 74 enemies right after jumping off a wall

Save the residents of Sector Five