Complex sentence: He ultimately heads back to Funnibones Warehouse disguised for more information, only to discover the knife that the Joker was holding the night he fell from the bridge; the Joker is not dead after all.
Split into simpler sentences: He ultimately heads back to Funnibones Warehouse disguised for more information, only to discover the knife that the Joker was holding the night he fell from the bridge. In the end, Batman discovers that the Joker is not dead after all.