"From up here we can drop rocks and arrows and more rocks!"
"Uh, yeah boss, but how do we get down?"

Goblin Balloon Brigade

{R}: This creature gains flying until end of turn.

"From up here we can drop rocks and arrows and more rocks!" "Uh, yeah boss, but how do we get down?"

30th Anniversary Edition

"The enemy is getting too close! Quick! Inflate the toad!"

The List

Conspiracy: Take the Crown

{R}: Goblin Balloon Brigade gains flying until end of turn.

Magic 2011

You can activate the ability repeatedly during a turn. This generally has no additional effect, unless some other effect (like that from Adarkar Windform has caused it to lose flying since the last time the ability resolved.

For flying to work as an evasion ability, an attacking Goblin Balloon Brigade's ability must be activated before the declare blockers step begins. Once Goblin Balloon Brigade has become blocked, giving it flying won't change that.