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:
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.