Ob Nixilis, the Adversary

Most planeswalkers with a copy clause bolt the doubling onto an activated or triggered ability; here the copying happens on the cast itself, and Casualty is what pays for it. Sacrifice a creature whose power matches X and you get a second Ob Nixilis, non-legendary and entering with X loyalty, so the sacrifice isn't a tax on the copy but a way to scale it: a bigger creature means a beefier second walker rather than a strictly better token. That structure resolves the usual tension a three-loyalty planeswalker faces, which is that it dies to a single attacker before it earns its cost. Two bodies split the opponent's removal and combat math in half, and both can start ticking their plus the turn they land. The +1 doubles as reach and hand disruption at once, forcing a discard or two life while feeding a life-swing if either half has produced a Devil, which the -2 obligingly does; the Devil's death-ping means even the tokens contribute damage on their way out. The card presents itself as a grind engine and behaves as a clock: one card that arrives as a pair, drains, disrupts, and manufactures its own board, with the casualty cost tuning how much of each you buy up front.