Decayer

Description
Launches shots along its row that inflict 10 damage and 20 on the player and 30 Poison on itself. Gains 40 and takes 5 HP damage when hit with a Spell.

Strategy
Weapons do not trigger the shield generation. and pierce the  generated by the Decayer. Single-hit spells like deal a lot of damage and almost ignore the 40 gained. Another possible way is to dodge the projectiles until the Decayer kills himself with the he inflicts when attaking.