Complex sentence: Gretchen is attacked by a creature similar to the spirit in the painting, which takes over her body and wears her skin; it kills Paul and Jay before chasing Jess, who breaks her leg.
Split into simpler sentences: Gretchen is attacked by a creature similar to the spirit in the painting, which takes over her body and wears her skin. It kills Paul and Jay before chasing Jess, who breaks her leg.