Sacrifice Play

Instant

A person outside the game chooses an attacking or blocking creature target opponent controls. That player sacrifices that creature.

2018-01-19:
You can choose any player not currently in your game. This includes people who used to be in your game but left it.
2018-01-19:
It doesn’t have to be someone who plays Magic. This may be fun.
2018-01-19:
If there’s no one around to make a decision, you can call or text someone if you need to. If there’s a physical action required, such as high-fiving, you’ll need someone there.