The first two are fought on Besaid and it is the island's toughest fiend. Due to its sheer size, Yuna is called on to summonValefor for the aeon's first fight.
The third time it appears is during a story sequence when the fiends attack Luca during the blitzball final.The Garuda here is slightly tougher, but Auron will be in the party for the first time since the start of the game, and the combination of his Power Break and Wakka's Dark Attack will make the fight quite easy.
After these two sets of story-related encounters, Garudas can be randomly encountered as a regular enemy on the Ravine Path of the Mushroom Rock Road. They can be found both during and after Operation Mi'ihen. Once again, they are a little tougher but blinding it makes all the difference.
Poison works extremely well against Garuda on the Mushroom Rock Road, doing a thousand damage every time it takes a turn.