Reverse bear-trap

Reverse bear-trap enters the battlefield with three time counters on it. (At the begging of your upkeep, remove one time counter.)
When Reverse bear-trap enters the battlefield attach
it to target creature you don’t control.
When the last time counter is removed, destroy this artifact, and attached creature.
Sacrifice another creature: destroy Reverse bear-trap. Create a key token (only the owner of the attached creature can activate this ability.)