As a quick idea for a feature request I think that it might be good to have an option to disable the OOC Regen on an NPC. This could either be done by a setting in the NPC_Types table or even better would be via a quest command that could enable or disable it on the fly.
Here is the code that sets the OOC Regen. To disable it, we would just need to add in another check in the if statement to see if the NPC should use the OOC Regen bonus or not. If we were just making a setting in the NPC_Types table, then this could just check that setting in the table. But, if there was a way to make a quest command to change it on the fly, I think it would be best, but am not sure exactly how to do it. Maybe setting a new field in the NPC_Types table and then make a command that can change that field in real time to turn it on or off.
npc.cpp
Code:
sint32 OOCRegen = 0;
if(RuleI(NPC, OOCRegen) > 0){
OOCRegen += GetMaxHP() * RuleI(NPC, OOCRegen) / 100;
}