Landorus, Thundurus, Tornadus, Latias, Latios, Moltres, Zapdos, Articuno, Raikou, Suicune, Entei, Terrakion, Virizion, Registeel, Regirock, Regice, Regigigas. I think those are all of them, but I'm not sure. Latios killed me last time because he was holding Bright Powder or whatever it was so my attacks missed. The main legends that I have trouble with are Latios, Landorus, Thundurus and Tornadus. I don't know how to beat them. I'd gladly use my own legends if I had good ones, but sadly I do not.

EDIT: I think most of what the legendaries use is here http://www.serebii.net/xy/battlemaison.shtml. Which means Latios would probably actually be using Lax Incense.

EDIT #2: Just acquired a 5IV (-SP. ATK) Jolly Terrakion from someone. Perhaps with that nice speed and attack he could prove useful?