Can Mystic Reversal be used to take control of an opponent's spell when you have no valid targets, essentially nullifying it?

Ruling: You can cast Mystic Reversal even when you have no additional valid targets. When you take control of the spell, you don't have to make new target choices - you can leave the original targets. If those targets are now illegal for you, the spell resolves with illegal targets and has no effect.

Sequence:

• Cast Mystic Reversal on the opponent's spell
• You become the controller of that spell
• You may choose new targets if legal ones exist, or leave the original targets
• If the targets are now illegal (e.g., the spell requires targeting opponent units but the original targets are your units), the spell resolves with no effect

Nuances:

• For spells with "up to X targets" (like Singularity with "up to 2"), you can choose fewer targets including zero when taking control
• Making legal target choices is only required when initially putting a card onto the chain, not when taking control of an already-chained spell