Gleam of Battle

Six mana for a buff with no ceiling: the trigger fires once per attacker, every combat, forever, with nothing in the text to cap how fast the counters pile up. Cast it pre-combat with a board already on the table and it pays off the same turn, every creature you swing with collecting a counter; the engine is only slow if your board is, because the whole payoff scales with how many bodies you can commit and how often you push them into the red zone. That is the tension the rate is buying. A single attacker earns a single counter per turn, so the card is feeble as a comeback piece and brutal as a go-wide multiplier, the gap between the two decided entirely by board state when it resolves. Vigilance compounds the math rather than gating it: a creature with vigilance still triggers the counter when it declares an attack, then stays back to block, so it grows turn over turn without ever exposing itself on the swing back. The Boros framing is the tell: this is a token-deck or aggressive-curve payoff wearing an enchantment's clothes, an effect that wants a flooded board rather than a single threat to grow. Its ceiling rides on whether the deck around it can keep creatures alive and swinging turn after turn, because the counters compound on a curve the opponent has to break before it runs away.