Fowl Strike

Green does not get to kill creatures freely, so when it does, the target is always narrow: a flier, the one board state the color pie has always let green hate. That restriction is the whole permission structure. Green's classic answers to flying were conditional by design (Plummet only touches fliers, Hurricane sweeps the sky and threatens your own life total), and this stays inside that fenced-off lane: clean destruction, but only against the creatures green is supposed to fear. The reinforce clause is what keeps the card from usually being dead. Against a grounded board the destroy mode is useless, so the discard-for-counters line folds an unplayable removal spell into a modest combat swing. That flexibility is not a bonus tacked on; it solves reinforce's oldest problem, which is that a pure discard-for-counters card is embarrassing when you draw it and the counters are all you get. Bolting a conditional kill onto the front means the card is rarely a blank in hand, and reinforce means the kill is rarely a blank on an empty sky. The result answers to green's restrictions on both ends: it can only destroy the creatures green is allowed to answer, and when there are none, it quietly becomes growth instead of sitting useless in hand.