Ostiary Thrull

The black body and the white activation cost are the whole point of friction here: this is a Thrull built for the guild-overlap of the era's multicolor block, asking a mono-black deck to find a white pip every turn it wants to tap something down. The effect is a defensive lockdown tool, repeatable creature-tapping that keeps a single attacker or blocker neutralized, but the design taxes it twice over. The Thrull has to tap itself to fire the ability, so it can only police one threat at a time and never both attacks and pins; it untaps as normal each turn, which means the lock is real but renewable rather than permanent. That dependency on a foreign color is what keeps a four-mana 2/2 with an evergreen control effect from running away with the board: in a deck that can reliably produce , it is a slow grinding lock; in one that cannot, it is a vanilla blocker with a dead ability. It is a quietly honest piece of multicolor design, the kind that reads as mono-black on the type line but only earns its rules text at the seam between two guilds.