Rainbow Island

If you have both Ho-oh and Lugia on your team, a cutscene will play where Ho-oh and Lugia chase eachother, and the trees or grass will turn rainbow. Then, you can battle Blue.

Battles: Blue (Lv74 Praxe, Lv75 Umbreon, Lv75 Machamp, Lv77 Gyarados, Lv77 Arcanine, Lv77 Exeggutor)