Keen Sense

Card advantage is canonically blue's domain, and stapling it to a single green mana on a creature you were already attacking with is a deliberate trespass across the color pie. This is the inversion that makes the design worth a second look: take the engine mono-green has always reached for in blue (the connecting attacker that refills your hand) and price it where green can actually afford it. The trade-off lives in the Aura itself. Sinking a card and a turn into a creature an opponent can answer at instant speed means a removal spell costs you two cards for none, the classic Aura tax that keeps the rate honest. So the card wants a target that survives combat and connects reliably: an evasive threat, a trampler too big to block profitably, or a creature you can protect. Connect once and the enchantment has replaced itself; connect twice and it is pure profit, which is why it reads less like a buff and more like a recurring draw step bolted to your offense. The trigger is generous in a way worth noting: it fires on any damage the enchanted creature deals to an opponent, not just combat damage, so a creature with a direct-damage ability that pings a player feeds it too. The single gate is that the damage land on an opponent, not on a creature or a planeswalker, which keeps the payout pointed at the work you built the deck to do.