Michael Myers, Evil Incarnate

At the beginning of combat on your turn you may sacrifice a creature. If you do, Michael Myers becomes unblockable and gains +X/+0 until end of turn. Where X is the sacrificed creature's power.
Tracking the victim — Whenever a creature with unblockable deals combat damage to a player, investigate.
Sacrifice 5 clues: Destroy target non-artifact creature. Activate only as a sorcery.