Let’s see what monster categories would probably be required.
Rodents
Birds
Deer (including moose and cows)
Bears (And Zombears)
Dogs
Vermin
Spiders
Snakes
Flying bugs (bees, wasps, mosquitos)
Crawling bugs (ants, mostly)
Slimers (Slugs and Sludge Crawlers)
Adult Fungaloids (regular fungal critters can just all be light whatever fungal colour you decide on (blue?)if it’s not used elsewhere)
Young fungaloids (unfortunately would prob. need to be different since the fungals tend to be mono color associated)
Triffids (Can all probably be the same even they they look super different, except the heart which could probably use it’s own tile, and maybe the queen)
Small Robots (Manhacks, eyebots, etc)
Large Robots (Securbots, Tank Bots, etc)
Turrets
And then the rare critters…
Nethercritters (Kreks, Migo, Blank Bodies, etc)
Shadow Critters
Snail Men
Amiga Horrors
Things
I think that’s most of them - it’s certainly a decent sized list, and then you’ll have to figure out how many color variations to put in…
Man, it really is a lot of work, and I think I’m missing some. Glad I’m not making a tileset. 