Description of NPC Death Loot Manager : https://osgmod.com/gmod-scripts/3915/npc-death-loot-manager
"NPC Death Loot Manager is my 5th GMod addon of the year 2021. It is about adding a gameplay mechanic to your server that is usually found in MMORPGs. It allows you to configure in real time from a clean and intuitive interface, the loot inventory of each class of Npc dropped when they die, choose the probability of dropping the npc, the quantity possible. All of this allows you to make items more or less rare from the list. For example you can set up special loots for a Boss."

https://www.youtube.com/watch?v=U72GBXDxlIA