Yasova’s ability checks to see if its parameters (Yasova’s power and its target’s power) have been met not once, but twice. Once when it is put on the stack (at the beginning of combat) and again when it resolves. What does this mean for you? More than you might anticipate.
First, it means you have a chance to boost your creature’s power in response to the trigger in order to make Yasova unable to gain control of it!
Secondly, it means you can’t trick the opponent into paying the 3 mana for the ability while also sacrificing your creature or making it an illegal target. Yasova’s controller puts the trigger on the stack and chooses a target. Then you have a chance to respond with something like Collateral Damage or Feat of Resistance. If you do, Yasova’s ability can’t resolve, so the controller won’t pay any mana, and will be able to spend it some other way. If you let the controller pay the mana, control changes before you get priority, so you won’t be able to cast Collateral Damage by sacrificing that creature anymore.
Today’s Rules Tip written by Daniel Clarke