Burning-Tree Emissary

The mana refund is the whole story, and it is a design that quietly rewrote what a two-drop could cost. The enters-the-battlefield trigger goes on the stack when the body resolves, and once that trigger resolves it hands back , regardless of how you paid the hybrid pips: pay and you still get , so the creature effectively costs nothing in mana once the trigger has settled. Deploy it, wait for the refund, deploy a second two-drop, and chain until a board appears out of what looked like one creature's worth of mana. The only real governor is structural: the summoning sickness on the body and the fact that you spend the turn to do it, because the mana leaves and returns rather than being generated for free. The refund is colored and use-it-now, which is what shapes the chain: it wants other red-green spells in the same window, not floating mana you can bank, so it has always been connective tissue for aggressive Gruul shells rather than a payoff on its own. The hybrid pips do extra work, letting both mono-red and mono-green builds run it without bending their bases. Few two-drops have produced as many turns where an entire board materializes for close to nothing, and the trigger has served ever since as the cautionary baseline for what happens when you refund a creature its full cost the moment it enters.