The Killer Clam is an unusual species, as far as monsters go. It wouldn't be called a "killer" at all, except people always try to pry them open. Why? Well, for the massive pearls of course (and any valuables the last pearl-hunter had on their person). Instinct: To eat

• Chow down on hapless adventurers

"They called me mad. Me! Just because I dreamed of a world made free from want! You see, if you could just feed poor people to magic boxes and turn them into gold, literally everything would work itself out . . . economics? What, no, of course I haven't studied them! I'm a wizard, not a businessman!" Instinct: To make meat into treasure

• Eat humanoids and digest them into gold coins
• It LOOKS like an ordinary treasure chest . . .

The white whale is ancient, exactly how ancient no one is certain. All that is known is that countless adventurers have lost their lives in the futile pursuit of this majestic, seemingly supernatural beast. Instinct: To be the master of the seas

• Crush something (a living thing or seafaring vessle) in its jaws

They were created as a more economically viable replacement for sharks with frickin' laser beams. Instinct: They attack instantly without provocation.

• They are very ill-tempered.

Cever is a tireless and canny assassin. He always wears a blindfold, a cardinals hat, and robes concealing his leather armor. He can move with great speed, always sure of every step. The shadowblade lets him move from shadow to shadow effortlessly. Instinct: To find, and to kill.

• Relentlessly track the Seekers
• Activate his ring of invisibility.

Psychovores are a vile lot. Fortunately, they mostly keep to themselves within Ferragrim, where they tend to the great beast's every need. In addition, they help it with the constant experiments: tending to the humanoid prisoners and keeping them in good health until they can be consumed and the husks used for recombination. Instinct: To consume intellect.

• Tend the Cerebral Brine
• Consume a brain and learn its secrets.
• Vomit forth Cerebral Brine.

[They] carefully entered the cavern, and were instantly assaulted by the scent of blood. The cavern floor [...] was deep with the creatures’ blood-red guano. (Tim Richardson, “Ecology of the Stirge”) Instinct: To suck blood

• Attach to an enemy
• Redirect an attack to its prey.
• Drink blood through its proboscis.
• See in the dark

Dingbat was raised by Deep Elves, but he does not share their passion for cruelty. No, he's walking the straight and narrow, he is. He's a real stand-up guy. That doesn't help with his chronic brooding, though. The man broods basically all the time, to the exclusion of other activities. In fact, he's SO dark and brooding that the heroes might understandably mistake him for an enemy. If this happens, they'll have quite a fight on their hands. Instinct: To find redemption, after brooding about it.

• Brood angstily
• Attack from stealth
• Summon a globe of darkness

More terrible than even the chaotic elder things are the gods who have gone wrong, driven mad by tragedy or for pain of being forsaken by even their own cults. A mad god is an unstoppable and ever-changing wave of pure destructive energy. Only those blessed by the gods can stand against the onslaught and stand any hope of success. Instinct: To un-create

• Unleash a wave of annhilation
• Conjure waves of destructive anti-angels
• Suspend a law of reality

"There are things beyond this realm, Jimmy. Awful things. Sometimes they get into our world . . . but just a little bit. If they came through all the way, we'd be dead for sure. No, they just . . . reach in. Test the waters, as it were. When that happens, sometimes they pull some unlucky damned soul back with them . . . god help us from ever finding out what those terrible, eldritch feelers are attached to." Instinct: To lash out at the physical realm

• Ensnare a living thing
• Release a miasma of madness
• Coordinate with other tentacles
• Emerge from shifting portals