Cast Volcano Hellion by paying {2}{R}{R}.
When Volcano Hellion enters, it triggers, dealing an arbitarily large amount of damage to you and a creature. The damage that would be dealt to you is dealt to Spitemare instead due to Pariah's Shield.
Spitemare triggers, dealing an arbitrarily large amount of damage to an applicable target.

Infinite damage to target opponent

Volcano Hellion

Pariah's Shield

Spitemare

Cast Wheel of Misfortune by paying {2}{R}, choosing an arbitrarily large number and having Wheel of Misfortune deal that much damage to Spitemare instead of you due to Pariah's Shield if you chose the largest number.
Spitemare triggers, dealing that much damage to an applicable target.

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