Sterling Keykeeper

Tappers are white's oldest form of soft control, and this one carries the lineage forward with a mercenary's price folded into the activation. Icy Manipulator did the work for artifacts; Master Decoy asked for a mana payment on a fragile body; this design lands in the same tradition, buying a repeatable tap for two mana each time rather than folding the cost into a one-shot. The two-mana surcharge is the tax that stops a repeatable pseudo-Pacifism from taking over a game: every activation is a real resource commitment, so its ceiling is a grindy, mana-flush stall where you can afford to fire it every turn and pin down whatever matters. It underperforms in the fast, tempo-driven games where holding up two mana every turn is a luxury you cannot spend, and where the 2/2 body would rather be racing than sitting back to tap blockers. The non-Mount clause is the era-specific wrinkle, a carve-out that keeps the effect from neutering a marquee mechanic while leaving it fully live against everything else. It reads like an aggressive creature and plays like a defensive lever: point it at the biggest blocker before an attack, or the biggest attacker before it swings, and let the mana math decide whether the tempo is worth the mana you sink into it.