Oerkki
In older versions of Minetest, the oerkki were hostile mobs that appeared only in dark places. They spawned underground, but had a low percentage of spawning above ground. They were not very menacing, as they would hover around and do 
damage, but would retreat if punched a few times with any tool/weapon (even bare hands).
Modern appearance
The Oerkki appears in three mods; Simple Mobs, MOB Framework and Creatures
Simple Mobs/Oerkki
This version features a more detailed 3D model instead of a flat sprite, as well as colliding with the player, but otherwise its behavior is mostly the same.
Oerkki is a hostile mob that spawns on stone in the dark and has same velocity as the player. It causes more damage than the dirt monster and dies in lava and water.
Creatures/Oerrki
Oerrki is a hostile mob that spawns only at night on stone or dirt like blocks.
They attack players and make more damage than Zombies or Ghosts.
Daylight can't harm them.
Mob Framework/Oerkki
Template:Mob
See the Mods/MOB Framework/Oerkki article.
Oerkkis are neutral cave mobs, they usually live deep down. Don't try to eat them.
When provoked it will cause damage ranging from 
to hearts.
Wood sword and punching do no damage to them.
To kill it you will need to swing 3 times with either stone, steel or bronze sword.
Faster 2 hit kills can be achieved with either mese or diamond sword.