Let me get this straight. Malfoy's a first year, just beginning his magical trainig. Harry's supposed to have all the power and spell knowledge from his alternate reality self. How could Malfoy cast such a powerful curse? Harry might toy with Malfoy for a while. But with the "complex wand movement" and long incantation (“Aquilus Avis Ignigena Ignipotens!”), wouldn't Harry simply shout "Expelliarmus" long before Malfoy finished? But more basically, how would such a curse be allowed? If "no one to date had survived it," wouldn't the ministry classify as an unforgiveable? After all, that can't be said about any of the unforgiveables, not even Avada Kedavra (which Harry survived).