Shadow of the Colossus/Avion - Colossus 5

This battle takes place over a lake, which is nice considering that falling off the colossus is in the nature of the battle. To reach the inner area of the lake, swim through the crack in the outer wall, then jump-climb up the ladder and approach the balcony. A cutscene will play showing the fifth colossi, Avion the Bird, entering the area. Drop down into the lake and find a platform to stand on. There should be one fairly close by. Once your on solid ground, equip the bow and fire at Avion as he's perched. He'll start flying around the lake.

For him to notice you, fire another arrow at him. Avion will come around and swoop down to attack. Getting on him can be tricky. Run and jump towards the base of a wing when he's close enough in his decent. This area is furry so grab on and climb atop his back.

The first magical weakpoint is at the very tip of Avion's tail. It's not hard to reach if he stays level, so feel free to run for it; however, I advise you keep a finger resting on the hold button, for if he decides to turn you'll fall of and have to start the process over. Charge stab the tail weakpoint until it disappears.

Run back to Avion's body and look towards the wings. Each one has its own weakpoint, but if your playing on Normal difficulty, you'll only need to take out one (Hard Mode requires both). Because these are his wings, Avion will flap them from time to time in order to remain in the air, which in turn makes it difficult to get a good charge shot in. Once you do manage a powerful stab, Avion will do a roll in the air and drain a good portion of your stamina in the process. If you're low on stamina, this manuever will likely send you falling into the lake, but if you manage to hang on, it only takes about two charged stabs to finish him off.