Umber hulk (monster class)
Some variants opt to further populate the umber hulk monster class, and may even repurpose it to add existing monsters. The biodiversity patch contains the umbral hulk and hunger hulk, pun-based variants of the umber hulk with gazes that can blind you or drain your nutrition, respectively; other variants may add umber hulk variants with similarly punny names and gaze attacks.
The shambling horror, U, is a monster with randomized stats and traits that appears in many variants, and is usually a part of the umber hulk monster class or its equivalent.
SporkHack is the first variant to include the shambling horror.
UnNetHack also adds the shambling horror to the monster class.
In dNetHack (and notdNetHack), this monster class is replaced by the unknown abomination, which uses the same glyph and includes the umber hulk as part of the monster class - unknown abominations are still designated internally by the macro
The shambling horror is one of three horrors with randomized stats and attributes that are a part the monster class; it also uses a different glyph, U, compared to shambling horrors in other variants.
EvilHack adds the shambling horror to the monster class.
SlashTHEM retains the water hulk from SLASH'EM and incorporates the biodiversity patch, including the umbral and hunger hulk. SlashTHEM also has the terror hall special room, which is populated by various hulks.
Hack'EM adds some monsters to the monster class, which are all imported from other variants: