Endoskeleton

Most toughness boosts are rented by the turn; this one is bought once and held. The +0/+3 persists exactly while the artifact stays tapped, and the clause that lets you skip your untap step turns a recurring activation into a single up-front payment: activate, decline to untap, and the bonus sits on one creature while your mana goes elsewhere. The friction lives in the swap. Moving the buff to a new body means untapping (surrendering the old bonus), re-tapping, and paying again, so the design quietly discourages chaining it across a board and rewards committing toughness to a single creature you intend to keep. Against a true Equipment, it cannot relocate freely and grants no power, but the trade cuts both directions: because the effect is continuous and bound to a chosen subject, it ends the instant that creature leaves the battlefield. Kill it or bounce it and the buff evaporates, tapped artifact or not, since the returning permanent is a new object the effect no longer recognizes. That makes it a defensive anchor rather than removal insurance: a way to lift one blocker out of burn range or off the bottom of a damage-based sweeper, paid for once and left in place. It solves one narrow problem (keeping a single creature alive through repeated stress) cleanly, with no ongoing upkeep and no power to dilute the toughness it is built to deliver.