When you set this scheme in motion, you may pay . If you do, this scheme deals X damage to target opponent or planeswalker and each creature that player or that planeswalker’s controller controls.
"Let that be a lesson to you, your family, and everyone you've ever known."
You choose the target opponent when the ability triggers. As the ability resolves, you choose a value for X and decide whether to pay {X}. If you do decide to pay {X}, it’s too late for any player to respond since the ability is already in the midst of resolving.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.