Sliver Overlord 
Legendary Creature — Sliver Mutant
: Search your library for a Sliver card, reveal that card, put it into your hand, then shuffle.
: Gain control of target Sliver. (This effect lasts indefinitely.)
Legality
standardNOT LEGALpioneerNOT LEGALmodernNOT LEGALlegacyLEGALvintageLEGALcommanderLEGAL