Your final confrontation with Vaas is a hallucinatory sequence. You'll be armed with a knife and must navigate a dream-like environment while Vaas taunts you. The key is to stay calm and follow the visual cues. Vaas will appear and disappear, often charging at you. You need to perform a quick-time event (QTE) takedown when he gets close. There are multiple stages to this, each more intense. Don't try to shoot him; the knife is your only weapon. Focus on the QTE prompts and be ready to react quickly. This fight is more about psychological endurance than raw combat skill.
