Shuko

The number that matters is the on the equip cost, not the +1/+0. This is Equipment you can attach and reattach as many times as you have priority and a legal creature to point it at, paying nothing each time, as often as the sorcery-speed restriction allows. That turns the act of equipping into a repeatable resource: a free "this creature was equipped this turn" trigger, fired again and again, with the stat boost reduced to incidental. Most Equipment makes you pay for the move, so the move is rationed; Shuko makes the move free, which is why the card spent most of its life as a combo piece rather than a piece of combat math. It powers creatures that care about being equipped, and in formats deep enough to assemble them it feeds untap-and-reattach loops where each free attach generates value with no mana ceiling. The is doing all the work, and it has shown up since in later zero-cost reconfigure and equip designs exploring the same logic: when attaching itself costs nothing, the attaching is the spell.