Complex sentence: As Christmas Future laughs diabolically, he pushes Scrooge who falls into the grave and desperately clutches at the sides to keep from falling into the casket, which belches out smoke and flame like a portal to Hell.
Split into simpler sentences: As Christmas Future laughs diabolically, he pushes Scrooge into the grave. Scrooge clutches at the sides to keep from falling into a coffin deep below, which belches out smoke and flames like a portal to Hell.