While they may not be the most dangerous of the q class, mumakil are a still a powerful threat that can do large amounts of damage. Mumakil have the most powerful single melee attack in the game other than the Riders', with their headbutt making a mockery of all but the sturdiest armor; their HP and AC of 0 also let them withstand significant punishment before succumbing.
When fighting a mumak, take advantage of its low speed—use ranged weapons, polearms, wands, spells, or hit and run. Mumakil have a thick hide, so they take no damage from kicks, among other things - while stronger characters like Valkyries or Barbarians may be sufficiently prepared for the encounter, mumakil tend to be a frequent cause of death for weaker or underprepared players trying to fight them in melee.
dNetHack adds a younger form in mumak calves, which can grow up into mumakil; they have the same difficulty and share many of the mumakil's stats, with the exception of damage, weight and nutrition value. Mumakil themselves are now higher difficulty and appear deeper into the dungeon.
In SlashTHEM, players polymorphed into mumakil or mastodons get intrinsic immunity to amnesia and improved spell retention ("an elephant never forgets"), the same as wearing an amulet of data storage. This feature originated in the Ring of Memory patch, which the amulet's function is based on.
Mumakil originate from The Lord of the Rings.
... the Mumak of Harad was indeed a beast of vast bulk, and
the like of him does not walk now in Middle-Earth; his kin
that live still in latter days are but memories of his girth
and majesty. On he came, ... his great legs like trees,
enormous sail-like ears spread out, long snout upraised like
a huge serpent about to strike, his small red eyes raging.
His upturned hornlike tusks ... dripped with blood.