Intervene

The narrowest counterspell mono-blue ever asked for. Its entire job is to protect a creature: it answers a kill spell pointed at your threat, the burn aimed at your blocker, the targeted bounce that would set your tempo back. It does nothing against a board wipe, nothing against a discard spell, nothing against the opponent's own creatures resolving. That hyper-restricted target clause is what earns the price; by refusing to touch the broad mass of spells a true counterspell stops, it becomes a cheap reactive shield rather than a control piece. The strategic axis it sits on is the bluff and the trade. Held up, it taxes the opponent's removal: do they spend the kill spell now and risk it being wasted, or wait? The instant-speed window matters too, because it can save a creature mid-combat from a trick or a burn spell, turning a clean two-for-one against you into a wash. The core idea here is older than most of the narrow protective tools that have followed it: spend almost nothing to make the opponent's removal disappear, and let the threat that survives do the real work.