This was only run on a state change and missed every external light change.
Any place which wants to flag a light change now only will set a flag and at the end of the thinker loop all flagged actors will be processed.
For performance reasons this was merged with the P_RunEffects iterator loop.
This was one of that annoying old design mistakes where Doom and Heretic features were poorly merged together. The Heretic Gargoyle uses very similar coding but performs a subtly different action when actually hitting another actor. This different action was made the default, even for the Lost Soul.
It has now been changed that both monsters use their original action, being distinguished by an actor flag. For compatibility with custom definitions Heretic's behavior, which has been the default in ZDoom will be the preferred one. The one of the Lost Soul can be reactivated by a flag.
Rearranged conditions to avoid accessing player from obsolete morphed pawn
Unmorphing upon death resets player in morphed actor, so player alive state should be tested first
Removed duplicate health check as well
https://forum.zdoom.org/viewtopic.php?t=65429
