Worldslayer

Connect with this Equipment and you don't win the game so much as end it: the trigger destroys all permanents except Worldslayer itself, and that "all" includes the creature that just dealt the damage. Your lands, your board, the attacker carrying the engine: all of it goes, leaving you with a naked Equipment and nothing legal to wear it. Pairing it with an indestructible creature is the cleanest way to come out the other side with a body still standing, and that requirement is the real cost of the card, not the mana on it. The double tax (five to cast, five to attach) is the second wall: by the time the engine is online you have committed ten mana to a board you are about to demolish, and the wipe takes your lands with it, so the rebuild starts from nothing for everyone. The whole design takes the symmetrical board wipe and bolts it onto the most conditional trigger in the game, combat damage to a player, which means landing the attacker, surviving whatever the defender throws at it, and only then razing the table. It is an early-era statement piece more than a functional removal package: an apocalypse button gated behind the requirement that you first walk a creature through enemy fire to press it, then find a way to keep that creature alive when the world burns.