Nice! I didn't even realize you could do that with eventhandlers! [apparently I had completely glossed over that fact when you posted it on the other thread -_-]
Revenant shoots own hitbox, so it has been blacklisted.
I take it that there's no precaution against when an imp is shooting at a target at a very steep pitch upwards? That's always been the reason why I've tended to avoid headshot actors.
This does not currently transfer ownership of kills to the player
If you use master.DamageMobj() instead of A_DamageMaster() (and use the hitbox's DamageMobj() instead of constantly polling hitpoints) you can specify the inflictor and source so that the monster is recorded as being damaged by whatever hit the headbox.
anyway, bumping because this deserves more attention than the other spaghetti headshot thread.