If Player 1 plays Dragon's Rage, Player 2 plays Defy targeting Dragon's Rage, and Player 1 plays Mystic Reversal on Defy, what happens?

Ruling: The player who plays Mystic Reversal gains control of Defy, but since there is only one legal target on the chain (Dragon's Rage) and Defy says "a spell" not "an enemy spell", they must still target Dragon's Rage with Defy.

Nuances:

• Mystic Reversal gives control of the spell to its caster, but does not allow retargeting if only one legal target exists
• Defy's targeting restriction is "a spell" rather than "an enemy spell", so it can target your own spells