Sawhorn Nemesis 

Creature — Dinosaur
As this creature enters, choose a player. If a source would deal damage to the chosen player or a permanent they control, it deals double that damage instead.
Legality
standardNOT LEGALpioneerNOT LEGALmodernNOT LEGALlegacyLEGALvintageLEGALcommanderLEGAL