Ulamog, the Ceaseless Hunger

The cast trigger is what makes ten mana feel guaranteed rather than aspirational. Exile two target permanents happens the moment you put the spell on the stack, so the disruption resolves independently of whether the 10/10 ever sticks: counter the creature, and the trigger still fires above it, taking your two best permanents with it. The targeting is open, not restricted to what the opponent controls, which means the trigger reaches any two permanents on the battlefield (your own included, when nothing across the table is worth answering). That single stack-ordering wrinkle reframes the whole investment. A finisher this expensive normally has to survive to matter; here the payoff has already resolved before anyone can respond to the body, turning the worst case into a locked-in two-for-one. The attack ability is the closer, not the threat. Twenty cards to exile from a library each swing is a milling clock that indestructibility protects: damage-based removal and most sweepers do nothing, so the honest answers narrow to exile or bounce, and bounce only resets the cast trigger to fire again on the recast. What the card represents is the high-water mark of a design idea that had been circling for years, that a spell should do its damage the instant it leaves the hand rather than after it arrives. The Eldrazi frame gives it a body worth respecting, but the real threat is the act of casting, and the 10/10 is almost a formality stapled to a payoff that has already happened.