{G/U}: Groundling Pouncer gets +1/+3 and gains flying until end of turn. Activate only once each turn and only if an opponent controls a creature with flying.
It matters that an opponent controls a creature with flying only as you activate this ability. Once you’ve activated it, Groundling Pouncer will still get +1/+3 and gain flying, even if all of your opponents’ creatures with flying leave the battlefield in response to the ability or after the ability resolves.