Mischievous Sneakling

In Commander, Mischievous Sneakling earns its slot in any deck whose creatures generate triggered abilities — attack triggers, death triggers, ETB-adjacent chains — because three mana for a blanket copy effect scales with every creature you add. Outside Commander, the card is legal across every major format but hasn't found a competitive home; triggered-ability-matters strategies in Modern and Pioneer tend to want more redundancy than a single three-drop copy effect provides. In Standard it's a fringe build-around at best, dependent on the current card pool delivering enough density to justify the slot. Pauper is the one non-Commander format worth watching — if a triggered-ability engine emerges at common, Mischievous Sneakling is already there and waiting.