Touchstone

A tapper, not a destroyer: this two-mana artifact spends its own tap to hold down an artifact you don't control, and that narrow verb is the whole shape of the answer. Tapping is delay, not removal, and the window it buys is small. The honest line is preemptive: catch a mana rock or activated artifact when you have priority (your own turn, or the end of the opponent's turn) so the resource is dark when they want it. What the wording cannot do is rewrite the turn structure. It does not stop an artifact from untapping, since the untap step happens automatically before anyone gets priority, so it cannot lock a permanent across turns; the effect lasts exactly until the next untap step and no longer. It also cannot interrupt an activation already on the stack. If a controller responds to your tap by firing the artifact's own ability, paying that cost taps the source anyway, which leaves Touchstone tapping an already-tapped permanent for nothing. So it works against permanents whose value comes from sitting untapped at a chosen moment, not against an opponent racing you on the stack. The text cares about control, not ownership, which fixes its job as a valve pointed across the table: it can pin an artifact you own but an opponent controls, and it can never touch your own. The narrowness is a fossil of mid-nineties hate design, from when one tiny effect against one card type read as a fair use of a slot.