Complex sentence: Eveline assaults Ethan with hallucinations, but he overcomes them and injects Eveline with the toxin, which doesn't kill her, but reveals she is the elderly woman in a wheelchair, who has been rapidly aging since her escape.
Split into simpler sentences: Eveline assaults Ethan with hallucinations, but he overcomes them. Ethan then injects Eveline with the toxin, but instead of killing her it reveals she is the elderly woman in a wheelchair, rapidly aging since her escape.