When using Mystic Reversal on Singularity that targets 2 of my units, can I choose 0 targets (since my opponent has no units) to effectively counter it, or must I choose at least one valid target?

Ruling: When using Mystic Reversal on Singularity, you can choose 0 targets because Singularity says "up to 2 targets" and 0 is a valid choice for "up to" targeting. This effectively counters the spell without destroying any units.

Nuances:

• Cards that require a legal target (like Falling Comet) force you to choose a valid target when using Mystic Reversal
• Cards with "up to" targeting allow choosing 0 as a valid option
• This interpretation is supported by other "up to" effects in the game (mulligan allows 0 cards, Sona/Annie can ready 0 runes)