Downdraft

Green does not fly, so its quarrel with the air has always been a grounding problem rather than an aerial one, and this is one of the cleaner statements of that color-pie position. Two abilities encode two different answers to the same axis. The first is maintenance mode: a repeatable grounding tax that strips flying from one creature for as long as you can pay the green, useful for pushing an evasive attacker through a blocker or holding the sky open turn after turn. The second is the panic button: cracking the enchantment converts the standing engine into a single burst of two damage to every flier at once. The tension lives entirely in that choice, because you cannot have both: keep it and you have an ongoing leash on a lone threat; sacrifice it and you trade the leash for a one-time sweep. The damage number is the tell. Two is small enough that it punishes go-wide swarms of X/1 and X/2 evasive bodies far more than it threatens a single large flier, which fixes exactly what this was built to answer: the cheap aggressive air force, not the lone dragon. It belongs to an early-design lineage of single-purpose hate enchantments, parked permanents that neutralize one slice of an opponent's plan and do nothing else, and within that group it is unusual for offering a graceful exit instead of just sitting there.