Crystallize is a Spell.
How to Get Edit
Cards with Endurance (i)Endurance:
Ready's on each player's turn, and can't be stunned or exhausted by spells or effects. will be unaffected by the Stun (i)Stun:
Exhaust a unit. It doesn't ready on its owner's next turn. (Exhausted units can't attack or block)., and it will be removed if they gain Endurance.
Cards with Endurance will still take damage from Crystallize.