Also, just for reference, creatures that appear in Mythruna will have a purpose other than just harassing the player. Like, where does some creature fit in the ecosystem and so on.
A notable exception might be the elementals like Takwin that are a byproduct of conditions and player magic... but even those have a deeper reason for being.
Minecraft is a fun game... partially because its mobs are one-dimensional devices... but they are still one dimensional and Mythruna won't be doing that. It should always be in every Mythrunian mob's list of choices to decide to run away because the trouble isn't worth it. At least in theory.
So probably:
-no player-seeking mobs
-no walking mines
-and generally, no "I popped into existence fully formed with motivations and everything just because the sun went down 10 seconds ago"
(If you get harassed by groo-lizards because you are wandering in the dark then that also means there must be a nest somewhere... and at any rate, they go and hide during the day and don't spontaneously combust.)
Minecraft mobs are like classic arcade game mobs. They are a single-mechanic extension, basically. You can almost trace them directly back to mob archetypes that existed in games as old as Gauntlet. (This is the one that beats on you in melee. This is the one that shoots you. This is the one that explodes under some condition. This is the one that teleports.)
Damn I was hoping for the walking mine type deal. Oh well it was worth a shot. I just was hoping for something that would explode and take a few blocks with it cause trying to dig a trench one block at a time is frustrating. Took me almost a real hour to make a peninsula into an island cause it was around 30 blocks deep and really long.
Having some sort of explosive something in the game would be nice. I figured a creeper knock-off would work well cause its already there and all you have to do is walk up to it and it explodes.
Oh well, Im sure you'll figure something out.