Scholar of Athreos

Scholar of Athreos is a Commander card through and through — the drain payoff only compounds over a multiplayer game where three opponents are each taking one damage per activation. In one-on-one formats like Legacy, Modern, Pioneer, and Pauper it's simply too slow; three mana per point of life loss is unplayable when faster, cheaper engines dominate. Pauper is its most plausible non-Commander home given the lower power ceiling, but even there dedicated drain shells have better options. Stick to Commander, and specifically to high-mana Orzhov builds where the card can fire multiple times a turn.