Labyrinth of Skophos

Colorless mana on demand costs a land nothing except the color it can never make, and this one pays that price to carry a fog engine stapled to the bottom. The lineage runs back to Maze of Ith, which removed an attacker for free but never tapped for mana; here the effect is metered by a four-mana activation and, crucially, reaches either side of combat. Removing an attacker keeps its damage off the table. Removing a blocker is the subtler line: the creature it had been blocking stays blocked (the phrasing does not repair that), but the blocker is pulled clear of combat before damage, surviving a trade it would otherwise lose and coming back around next turn. The cost structure carries the tension: the mana ability keeps the land from being a dead slot, while the four-mana tax makes the combat lever a late-game tool rather than an early-game one, and "remove from combat" sidesteps indestructibility and regeneration without ever putting the creature in the graveyard. The net is a colorless, cardless answer that resets a combat step from either chair, over and over, as long as four mana is spare.