Boromir, Warden of the Tower
The trigger half is the piece worth studying. "If no mana was spent to cast it, counter that spell" is a narrow, surgical clause that reads like a curiosity until you count how many of the game's most dangerous plays route around the mana system entirely: free spells cast off exile-based alternative costs, cascade hits, pitch-cost combo pieces that make fast decks fast, the zero-mana engine that never touches a land drop. This does nothing to a normal curve-out; it triggers specifically on the plays that cheat the mana cost, and because it is a "whenever an opponent casts a spell" trigger, the answer sits on a body already in play rather than a reactive spell you have to hold priority for. That is the design tension: the effect belongs to a control player's toolkit (a permanent-based tax on free spells, close cousin to what Grand Abolisher does for a different problem), but it is stapled to a vigilant creature that wants to be attacking. The sacrifice line resolves that friction by giving the body a graceful exit: cash the Warden in for a one-turn indestructible blanket, protecting a swarm through a wrath or forcing bad blocks. Read together, the two halves sketch a soldier who guards until the moment he is spent defending everyone else, about as tight a mechanics-to-flavor fit as a legendary gets. The spine, though, is that free-spell counter: a white answer to a problem white almost never gets to touch.
