SCRAP PRINCESS ENGINEERED THE ST. PIERRE SNAKE INVASION

I'm not saying that she bred all of the snakes personally, but she definitely was in St. Pierre, throwing snakes at children.

ANYWAY

Dinosaur
Psychosaurs

These are hyper-evolved dinosaurs from an alternate timeline.  They're giant flying dinosaur heads with psychic powers.  They refer to humans as "foolish mammals" and like to cut our heads off, then make fun of us when we die.

Wherever there is one psychosaur, there is always another, because they travel through time almost exclusively to create advantages over other psychosaurs, and to foil other psychosaur plots before they become manifest down the timeline.

Displacer Beast
Beast of Singular Intensity

Once you enter its floor of the dungeon, you become instantly aware of it.  It's like you've been using a singular computer monitor your whole life, and then suddenly, a second monitor flares on beside it.
Once you are aware of the Beast of Singular Intensity, you cannot back away from it.  You can approach it, and you can circle it, but you cannot leave until it is dead or placated.  This whole floor of the dungeon is annular, and the concentric rings are full of other creatures who have chosen to circle the Beast rather than face it.

It looks like a cross between a cobra and a cicada.  It rises from a mossy pit.  It has no eyes but it has many Eyes.

Dog
Terrible Tumor

Sort of like an angry baby that is growing out from the base of your neck.  It whines and harasses and if it gets really frustrated it will start throttling you.

You can't remove it without killing yourself, and any damage it takes is mirrored onto you.  For example, if you cut off its arms, you can no longer move your arms.  If you bind it, you can't move either.

What does it want?  Liquor (you get drunk, too, since you share a bloodstream), to dabble in the darkest of magics, to commit unspeakable perversions, and to scare people.

Djinn
Flim

Creatures of fireless smoke, flims are utterly powerless.  They look like they can fly, and yet they can barely crawl.  They are so fragile, a determined Corgi could kill one.  They have terrible eyesight and weak voices and although they can carry small things like papers and gems, they must take breaks.

Neither Good, nor Evil, nor Neutral, they're just sort of there.  They struggle to understand and affect the world around them, and so they tend towards depression and lethargy.  They sigh a lot.  You could do a lot to help one, and it would be grateful, but then what?

Dolphin
Orb Snail

Picture a sphere on the bottom of the harbor.  The sphere is about seven feet in diameter, and it appears to be made from rock or shell.  It has semi-hexagonal scutes, like a turtle's shell.

On the side of the sphere is a crusted gap, big enough to fit your head inside but not your shoulders.  It is from this hole that the orb snail can extrude an organ.  Here is a list of the possible organs that the snail can extrude.

• A muscular arm, good for grabbing things and drowning them.
• A muscular foot, good for gripping the ground and creeping along.
• An turgid eye on an enormous stalk.
• A sphincter-like mouth, capable of spitting a weak acid.

If Gygax wrote this, it would probably kill adventurers by rolling them over on hills.  And while yes, orb snails can kill you like that, they much prefer to just drown you.

It is actually a species of turtle.  Everyone is wrong.

Dragons

They deserve their own post.

Dragonne
Hog Dragon

Bred by goblins in order to debase and humiliate dragons.  Obese, foul-tempered, slothful, and immensely strong.  Stats as a dragon, except Defense = Leather.

Stench -- Can produce a stinking cloud every 1d4 turns.  Within 50', the stench is so strong that materials become soft.  Metal becomes rubbery.  Stone becomes like mud.

It's weaknesses are its temper, its appetite, and its tireless stupidity.

Dragon Turtle
Angeloid

A soft, flying thing, all gossamer and molasses.  Like panes of brown and yellow glass being shuffled.  A face that is eternally flopped to one side or the other, like a dog's.  It wants to take you places, show you things.  It will trade things, but it only deals in intangibles.  It'll identify a magic item if you feed it all of your memories of your father (lose a point of Wis).  It'll carry you anywhere you wish to go if you let it wrap your courage in an eggshell and carry it away (-4 vs Fear).

Dryad
Gurgans

Horrible, shriveled man-things.  They squat, lurk, snivel, sneer, grovel, and beg.  They're horrible and pointless.  They own nothing useful; they never know anything relevant.  Killing them gives you a negative amount of XP.  Their livers are painful and distended and they can curse creatures by spitting on them.  If you kill one, you may turn into one yourself.

They're usually found sleeping in front of a doorway that the party needs to get through.  Or they demand to be carried to a different part of the dungeon.  Or they demand food and compliments.

If these demands are not met: curses.  If you attack them: curses.  If you ignore them and make them feel the suffocating weight of their own crushing loneliness: curses.