Complex sentence: Remembering his true self and what Bruttenholm brought him up to be, Hellboy breaks his horns, reseals the Ogdru Jahad and stabs Rasputin with one of his broken horns.
Split into simpler sentences: Remembering his true self and what Bruttenholm brought him up to be, Hellboy breaks off his horns, returning to his former self and resealing the Ogdru Jahad. Hellboy stabs Rasputin with one of his broken horns.