Xanathar, Guild Kingpin

Description

Xanathar, Guild Kingpin (PRM-92788) is a legendary Beholder creature from the Magic Online Promos set. Its beginning-of-upkeep trigger targets an opponent and, until end of turn, bars that player from casting spells while letting you look at and play or cast the top card of their library and spend mana as though it were any color to cast those spells. That combination of disruption and access to opponents' cards makes it useful in control or theft-focused builds.