We've seen this guy get shot in the head, and he has slit his own throat. What would it take to actually kill him? Can he be killed?
If he was beheaded, would the two halves continue to "live" as separate entities? Or would his head start to regenerate a body, or would the body start to regenerate a head?
Could Parrish control his body while his head was detached?
A strong dose of poison might kill him several times, but it would eventually lose its potency and he would wind up staying alive.
Fire? Acid? Could he regenerate from these?