There are already some topics on the subject, zombies? Drone? Others?
In my opinion it is always cool to have a large bestiary that can have the same appearance but not the same attributes.
I will quote the game dead in the bud "Fear the night" it offered a significant diversity of zombies
For example, there was the classic zombie; slow, humanoid, having a chance to unhook his body once on the ground and attack you a few more seconds after shooting him.
There was the goul; creeping, fast, unpredictable jumping on you to tear you apart
There was the explosive zombie, big and staggering kamikaze
the determined reinforced zombie, massive and seemingly invincible
But on the other hand there was robots some just passiv but act like alarm (dogs) other more aggressive that defend PoI or Area both was able to be tamed/hacked to be part of your Entourage/team to carry stuff , defend you or your base , attack enemies or peoples
We can imagine area where zombies come from the underground (cemetery , waste dump …)
On “scum” there is some NpC , robots and puppets
On anyway it’s pretty sure that “classic zombies“ as only “living threat” isn’t enough.
I’m sure you already think about that and again you certainly will find ideas on other title (arc riders / ark / scum / fear the night*
*even if it’s a dead game in the egg please check what they done on the past 🙏👍👍