This is for any version of DnD or clone and for DM or Player alike.
As a DM a monster you've used.
As a Player, monsters you've fought or interacted with.

Having run or played DnD on and off since the early 80s, I've used quite a few of the DnD monsters from the Monster manuals, fiend folio and other MM type books in various DnD clones.

I'm sure there's loads of monsters I've not used that I've wanted to, but the main one that springs to mind is:
The Beholder..
Mainly as they're so darn powerful and you'd need a high level party to even have a chance against one.

But they are fascinating. I'll probably stick one somewhere working behind the scenes in some underground or hidden part of a city, like a crime boss or something. That'd be cool.
Perhaps when the party is strong enough build up a scenario that ultimately leads to a confrontation with said Beholder boss.
 
How about you?
What monster have you been dying to use/fight but never got a chance too?
and why?

The little-known variant (mainly because no one survives)... Blood Flumph!

Beholders are almost like the orcs of Spelljammer. Really common foes in it.

Actually, though, when I was a kid, I don't think there was much we didn't kill in the MM, MM2, and FF. We went through a lot of D&DG as well.

My recollections are vague, but I distinctly remember killing King Arthur to get Excalibur. And then a bunch of Central American gods, because they were easy to get to (in a parallel material plane). I think we went through the Chinese mythos first though, that's where we got the idea. If Ma Yuan can kill gods, why not us?

While not a "classic", every since I read their descriptions, I've found the Inevitables interesting.

The highest we've ever had a D&D campaign reach is level 10 (and a TPK happened almost immediately on reaching 10th). So there are a great many classic monsters I've never used. Liches. Beholders. Ancient Dragons. Most Demons and Devils.

If I had to pick one I'd like to use it would be Pit Fiends. They just look so cool (as depicted in the AD&D MM), and have such a terror-inspiring reputation.

Quote from: Haffrung;796426The highest we've ever had a D&D campaign reach is level 10 (and a TPK happened almost immediately on reaching 10th). So there are a great many classic monsters I've never used. Liches. Beholders. Ancient Dragons. Most Demons and Devils.

If I had to pick one I'd like to use it would be Pit Fiends. They just look so cool (as depicted in the AD&D MM), and have such a terror-inspiring reputation.

I'm in the same boat as you.  However, rather than TPK, we typically just retired the PCs in the low teens because we wanted to play something different.  So I don't recall ever going up against a beholder or lich or arch-demon in the past 30 years.

As I run DnD for my kids, we tend to play that in evenings instead of other stuff like TV, computer games, consoles, whatever else.

As a result of that, we're really churning through the 5E MM atm.

They're at level 5 now and I've most recently run an interim homebrew adventure in a swamp, using Hags, Ettins, Lizardfolk (who are sort of allies of the characters atm).
Plus Shambling mounds, Water weirds and a load of other monsters.

There was a sort of territorial battle in a swamp between a tribe of Lizardfolk and some Hags that wanted to muscle in on the Swamp as a Ley line Nexus point appeared (due to a big event elsewhere), which is a good magical power source.

They just finished that adventure last night actually in a grand finale battle at the Ley line Nexus point.
The Black hag was trying to corrupt a waking up Treant with her Heartstone that was powered up by the Nexus point.

It was a pretty epic battle and with the help of the Lizard folk, who had a lot to gain by eliminating the Hags, they were triumphant.

Now that's done, They'll be back onto the way to Nulb and the Temple of Elemental Evil to continue their adventures, where I'll get to use more monsters for them to battle.

Crypt Thing.

Always thought they seemed cool.  Even put one in a dungeon, but nobody encountered it.

I'm pretty sure I've used every monster I want to.

Intellect Devourer: They were absolutely brutal in AD&D.

The 5e one is pretty mean too.

Golems: Aside from a Brain Golem I've actually never used one before. I had a really awesome Clay golem mini I made way back but never got to use it.

Apparatus of Kwalish: Not a monster, but I've allways wanted to spring one of these on a party, piloted by the villain... or some kobolds...

i dont think i would be suitible for puting my players up against a beholder i would play it to well

things that are suposed to be brutes i run as brutes but if there description says they use tactics i pull out all the stops

i recently had to let my players get away with a lot of bending of rules because i had started the fight against the kobolds to well and had to switch them from wisely using there slings to running in with spears

that said i think the only reason they did not decimate the cleric was because of some unlucky rolls

i would just follow the descriptions of what eye beams the beholder would use for what enemeys however i would make sure the beholder brought as much to bear us it could when you look at its rules in the 3.5 monster manual it can quite easily fend of most attacks and it can attack both its front and behind it plus it can aim its main eye wherever it wants each turn