Rotmound
Rotmounds are mounds of waste brought to life. Each takes on properties from the place it lives in, but they nearly all fight the same way.
You find them at Castle Morne, where one even clings to a prison cell ceiling, and bloody ones in the Writheblood Ruins and the Mohgwyn Dynasty Mausoleum in Mohgwyn Palace. In the Realm of Shadow there are putrescent ones in the Stone Coffin Fissure and red lightning ones on the Jagged Peak.
Drops
Weaknesses
Resistances & immunities
How to beat it
Rotmounds like to wait on ceilings and drop on you. In Castle Morne, one sits above the corpse holding the Pickled Turtle Neck in a prison cell: grab the item and step away fast, or it lands on you and takes a big chunk of health.
Since all variants share the same moves, once you learn one you know them all. Just respect the element: blood, putrescence or red lightning.