Invasion of Karsus // Refraction Elemental

(As a Siege enters, choose an opponent to protect it. You and others can attack it. When it's defeated, exile it, then cast it transformed.)
When this Siege enters, it deals 3 damage to each creature and each planeswalker.
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Ward—Pay 2 life.
Whenever you cast a spell, this creature deals 2 damage to each opponent.