The impostor was a criminal from a secret criminal organization in outer space. They were sent to kill the crewmates and sabotage the place. When all the cremates are dead or defeated they'd steal valuables inside the place and take it to their organization. They have a suit to wear to impose a crewmate they killed or tortured. The reason why they look act like a monster is that they have monstrous gadgets. They have the knowledge to vent but the crewmates do not have the knowledge to. They sabotage the ship so while the crewmates are fixing what the impostor sabotaged the impostor could do killing while the crewmates don't see what the impostor is doing. AMONG US IMPOSTOR; SAW; shapeshifting alien that has long spear tounge can survive without o2 has weirdo status when getting scanned can survive lava