The Dakon isn't too complicated, but, really, it doesn't need to be. It's an intelligent, lawful neutral ape. There are about a million more interesting things you could do with an ape.
Anyway, now the truth can be told: the Dakon are actually monkeys and they're chaotic evil. They can be distinguished from ordinary monkeys by the fact that they cannot see a pig without being compelled to ride backwards on it.

The only problem is you don't want your players going "oh another thing that looks like a person only shorter and uglier and with some bizarre aversion to levelling up" So here's my take: everybody talks about Dark Creepers, but, like Grues in Zork, no-one has ever seen or described one.
"Oh, the Caverns of Grool! Go thee not hence--Dark Creepers abound! In the night they come, creeping darkly! Fearful and felonious are they!"
"Dark Creepers? What are they?"
"Horrible night creatures!"
"Yeah but..."

Same for their built-in boss-species, the taller, svelter, explodes-fireball-force-when-killed Dark Stalkers...

But I just can't ignore a two-headed dog. First: because this, second: because "two-headed dog" is one of those things that homicidal maniacs see when shown rorschach blots and so can be used by shrinks to separate people trying to fake a not-mentally-fit-to-stand-trial defense apart from genuine psychopaths (and people who read this blog), third: because I love saying "two-headed dog".
So here's my way around this example of Gegenstandsverdoppelnde:
Ever notice how no matter how many dog-monsters they make it's always the same dog?

-an inability to talk about anything other than their dogs,
-an inability to notice any problems associated with their dogs--be these ailments, behavior problems, injuries, or the fact that they have two fucking heads
Oddly enough, keepers of Red Temple Dogs do often give their dogs two names (often wildly inappropriate ones), and use them indifferently, though they seem to be wholly unaware of this.
The animals themselves are indeed deadly, though they refuse to hunt in packs.
Next up is the Death Knight, and the only real problem with the death knight is that it's hard to make a picture anywhere near as cool as the original.

Pretty much exactly the same goes for Lolth...

On the other hand, the Denzelian is as mad a spasm of uselessness as has ever answered "Nil Nil Nil" to the Lake Geneva Standard Monster Manual Interestingality Inventory. Sayeth Jeff: " A super-slow non-hostile slime monster whose only function is carving tunnels around metal deposits. Sure, I could write some sort of scenario involving competing mining interests and a stolen denzelian egg, but I'm not sure I really want to." Yeah, mining is even mentioned in the entry. Mining is right after farming, pretending you are a mormon and having a relationship requiring even more talking than one(s) your in in real life on my list of things that get put in games for reasons I only dimly understand.
My denzelian hack is this: the beast...
-can only tunnel straight down,
-does so about as fast as the Alien's blood does in the Ridley Scott one,
-is intelligent,
-is chaotic neutral,
-eats gold,
-understands and can telepathically communicate in the common tongue, and
-has a metabolism allowing it to dissolve d2 levels of dungeonrock per 600 gp of gold it eats.
-it can live in condensed form in suspended animation a specially-prepared alchemical container for up to three years, awaking only to feed on sheets of gold leaf once a week.

Styx Devil. COMESailaWayCOMEsailaWAYComeSAAAILAWAYWITHMEEEEE. Ummm, sorry...
"Their main task is to search for souls to take back to Geryon, but from time to time they will tour the Material Plane with intent to destroy all humans they meet."
This second bit would be an awesome job description if it wasn't what everybody else in the Fiend Folio was also doing. It's like saying "Yeah, we know 'Styx' means something in like, mythology, but also this is a monster".
Its encounter schtick is it casts an imprisonment spell and you defeat it with a holy word. So fighting it is one moving part less exciting than playing rock-paper-scissors.
Anyway in my infinite wisdom and desire to turn a South Park subplot into a monster hook I have decided that actually the thing is that the Styx devil strikes only those who are resurrected, reincarnated, et cetera while they are in the underworld. Its power is it can implant a message (an incantation, an invocation, a song about sailing etc.) in a victim's mind. If the victim hears a trigger phrase (usually the first word or two of the text) s/he must then speak the entire message.

We need a total overhaul.

Dire Corby. Oh the sucking. Luckily I have a fast out all ready to go: it's not dire, it's just a corby and its a subhalfling-sized flightless crowman that sneaks around dungeons trying to steal PCs stuff while they sleep.

However the word "disenchanter" is good. And the magic-removing mechanic is totally monsterable. And I have always wanted to turn my dim and unconsciously anthropomorphized memories of the cover art for the game "Enchanter" (which I never played) into a picture.

Doombat: the doombat's not so bad on paper, the only thing is your party is probably already facing regular bats, giant bats, lots of things with bat-wings and the occasional vampire so it needs more of its own thing than "shrieking and tail barbs" to not just be a rerun. Taking my cue from the fact that Doombat sounds like a name an overconfident megalomaniac idiot wizard would make up ("FLEE BEFORE THE LEATHERY FURY OF MY DOOMBATS!") I decided it was one of those crazy alchemist inventions.

Dragon, Oriental: I spent way too much of my youth earning sodapop money drawing white trashy tattoo flash to have any enthusiasm for drawing every one of the Folio's boring and underdifferentiated oriental dragon variations (Earth, Water, Coiled, Spirit, Celestial and Carp), plus, the idea of this project is that I am making these monsters usable in my game--and the fact is dragons are way too fun to spoil them by using more than one or two per campaign. So I'd be lying if I said thought I'd ever get around to using all these.
However, I will use the names. An asian campaign is not an asian campaign without government officials and wise men constantly referring to obscure and unseen Dragons of the Wind Gate and what-all constantly.

Dragonfish: "Dragonfish are 2' long, mottled brown flatfish" THEN WHY ARE THEY IN MY GAME??? Dragonfish? Dragonfish? That is not a dragonfish, that is a fucking flounder with stalagmites. This is a fucking dragonfish:

Dune Stalker: Big eyed naked ghoul-man who kisses you in the desert and so then you die. Creepy enough, bad picture. So I did a new picture:
