Altar of Shadows 
Artifact
At the beginning of your first main phase, add 
for each charge counter on this artifact.
, 
: Destroy target creature. Then put a charge counter on this artifact.
Legality
standardNOT LEGALpioneerNOT LEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL