SPECIFIC.IDS (?)

[Lu_]

Its values are used in .CRE files. What are they for?

In BG2 they are normal/magic/no_magic, but in most files it's set to '00 unused'

[Avenger]

specific ids are not hardcoded in the engine, thus their usage is entirely in the data content. I don't think anything in the original Bio games actually used them even if 2-3 values have been defined in specific.ids. EE games do use them much more.

The good thing about specific is that it can be used from scripting and effect opcodes too to make arbitrary groups of creatures.

 

You could define a value that marks water breathing creatures, then create a spell that affects only water breathing creatures.

Or you could mark a group of creatures as "Black Hand Kartel" and despite they could be mages, thieves, fighters or even player characters, they could still recognise each other easily enough that they will help each other in combat scripts.

[Ardanis]

It's used in InMyGroup() trigger, returning true if both the object and the script owner share the same specifics value. EE games use these values to label various creatures as belonging to various factions, e.g. Sharrans and Deepstone dwarves.