You get Crusader when you defeat all the legendary dragons. You may have to defeat Skull Dragon last, since that's when you're supposed to get it. Anyway:

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CRUSADER Attack harms you and the enemy
PURIFIER MP Cost: 96
Deals high non-elemental
damage to all characters
on screen.


Merton Learn Rate: x 1
Meteor Learn Rate: x10

At level up... MP + 50%

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