Hm, that's a good thought... like just multicolored bases of some sort, and you can decide what different colors mean however makes it make more sense. I know you can get different colored plastic rings on Etsy and etc that are designed to snap around a mini / token and indicate different things about the creature, also.

I just recently started doing brass bases for some of the player tokens; in my mind they were going to be super popular and it would solve the problem automatically, because the creature tokens would have a totally different construction so it would be immediately apparent, but it seems like people are still into the wooden tokens for whatever reason 🙂.

One other idea which I think I might incorporate at some point is Sly Flourish's using letters for creatures and incorporating damage with the letter -- maybe I'm not explaining it well, but I really liked the idea:

During the game, when a character damages a monster, ask the player to identify an interesting physical characteristic of the monster they hit that starts with the letter of the token. Thus, the ghoul represented by the skull A token becomes the "ghoul with an arrow in her head". This way you have an in-game narrative that connects the story of the monster with the token. Skull A is a ghoul with an arrow in her head. Skull B is the ghoul with the bones sticking out of his back. Skull C is the ghoul with the caved-in chest, and so on. This is far better than fighting "ghoul A".

I actually have some vague plans to switch over to using letters for groups of creatures for exactly this reason -- this might be an idea that makes it easier to keep track of which creatures are badly damaged also (because the players have a lot more vivid conceptual reference of which one is which in their minds).