tl;dr: Cool mod that adds diverse slimes for different biomes. Crashes Minetest on 5.3.
For an easy fix find the .lua files for each slime in the mod's slimes folder and comment out this line wherever you find it:
So it looks like this:
The Longer Review:
This is one of the more immersive creature mods you can add to your world. It makes your survival world feel more alive. Most of them aren't really a huge threat, but they can still put up a fight.
Recommended for anyone looking for a unique hostile mob mod, especially if they grew up playing old Japanese RPGs like the Final Fantasy series, or, indeed, The Mana World.
As is, the mod crashes your game on 5.3 – something to do with their animations and mobs_redo. Sadly, Piezo_ is not currently active in the Minetest community, so it is unlikely to be updated directly...but you CAN get it to work if you’re not too afraid to alter the code slightly.
Longer explanation of how to fix it (thanks to FreeGamers on the Minetest Forum):
Go into your Minetest mods folder and find the folder for twm_slimes, then find the slimes folder inside that, you will see several .lua files named after the different types of slimes.
Open up these files in a code editor and comment out the following line anywhere you see it:
In LUA, you do that by adding this – before the line you need to comment out.
Save your files and try enabling and playing with the mod now. It should work now!
It's not a super clean fix, but it will let you use this quality mod. Plus, by fixing it yourself, even with these little tiny steps you are learning how easy it is to make your own mark on Minetest and have proper control of your game.