Tui-Tui-Sem, the Beast With Three Heads

Wild-eyed prospectors and far-ranging scouts alike tell the same tale of the badlands - a massive, three-headed beast, appearing out of seemingly nowhere, descending upon their party and devouring both pack animals and whichever men and dogs fled too slowly.

This creature - thankfully unique, so far as anyone can tell - is called Tui-Tui-Sem in the tongue of the Black Eagle tribe (1).  Translated loosely, its name is "Chew, Chew, [and] Chuckle".  The beast is the size of a mammoth, and covered with barbed quills which practically drip with deadly poison (2).  Each of Tui-Tui-Sem's three predatory heads sports three eyes and a maw with dual rows of sharklike teeth (3); typically two heads face forward whilst the third scans behind the creature for danger (4), or prey.  Four massive legs end in sharp black talons which Tui-Tui-Sem uses to carve up its prey into chunks suitable for eating (5).  A rat-like tail drags behind the beast.  Dr. Hornapple of River-Town has studied the lore extensively and has come to the conclusion that Tui-Tui-Sem possesses a natural or supernatural ability which makes it invisible under certain circumstances (6) - this of course only increases the beast's lethality and reputation.  The creature's growling call is said to resemble human laughter.

This three-headed monstrosity will gladly attack and eat any living creature it encounters, but it greatly prefers the flesh of felines to any other meat (7).  Strangely, there are multiple reports that Tui-Tui-Sem fears the color green, or a particular shade of it, and will flee from it if boldly brandished or waved and accompanied by shouting (8).  Dr. Hornapple is of the opinion that not only is Tui-Tui-Sem a singular beast, but it is perhaps immortal, the hideous offspring of some some forgotten demigod or devil (9).

GM NOTES
(1) - Of course, the Black Eagles do not live in the badlands, but no doubt some of their warriors encountered Tui-Tui-Sem during raids against the Vulture-Men or the Cloud Rabbit tribe.
(2) - Although Tui-Tui-Sem does not use the quills offensively per se, it should be noted that the toxin is classic 'save or die'.  This is a legendary beast, after all.
(3) - The immense, triangular black teeth are sometimes found in the wild, and have value for sorcerors, as they make a fine component for spells involving sharpness or blood-letting.
(4) - Tui-Tui-Sem should be harder than usual to surprise with whatever surprise rules you're using.
(5) - Damage as per scimitars.
(6) - Tui-Tui-Sem only fully exists in our realm during the height of day; in the dark of night he roams some other plane.  In the early morning twilight and the gloaming of dusk, he straddles these two worlds, and is invisible until he attacks (as per the classic spell), manifesting fully in our world.
(7) - The beast has a keen sense of smell and will preferentially attack felines or persons who smell of felines.
(8) - Using a bright green cloth or other sizeable item, a fiercely-shouting person can attempt to turn Tui-Tui-Sem as a cleric of equivalent level (or 1st if the person has no PC levels); treat Tui-Tui-Sem as having 9HD for this purpose.
(9) - Probably true; Tui-Tui-Sem will be affected by magics (or magic weapons) which do extra damage to either fairies or infernal spawn.

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"It's a monster with three heads.  He has three eyes on each head and spikes all over his body.  He's invisible and eats you up like NOM.  He likes to eat cats, but he hates the color green.  His name is Tooey Tooey Sem because he has three heads.  Tooey, Tooey, and Sem."  --The Boy, age six

Anybody feel like sketching this horrendous thing?