Re: NPCs don't follow the same rules as PCs, never have in 5e, and that's ok.
Originally Posted by Kuu Lightwing
Well no, but they will probably notice if spellcaster flies into rage. And besides it's not just a player perspective discussion, though it is considered too.
Which is an excellent point. I don’t see anything wrong with players learning about the opponent and then figuring out how to deal with them.