Helm of Possession 
Artifact
You may choose not to untap this artifact during your untap step.
, 
, Sacrifice a creature: Gain control of target creature for as long as you control this artifact and this artifact remains tapped.
Legality
standardNOT LEGALpioneerNOT LEGALmodernNOT LEGALlegacyLEGALvintageLEGALcommanderLEGAL