I'm setting up an adventure with minions of the Egg of Coot (though I'll probably use a slightly different name).

DA1 says the Egg has human minions and a "lich lord". So there are probably other undead (a lich lord would presumably command weaker undead).

What kind of living "monster" minions, other than humans/demihumans who have fallen under its influence, would the Egg likely have? I'm looking for stuff suitable for mid-level characters. I have lots of undead lined up, but it shouldn't be all-undead IMO.

As part of the MMRPG there are two adventures that can be connected between them and that may be useful for you: Ties that Bind (at the end of the campaign setting book) and All the Egg's Men (episode 35).
You'll find not only monsters and enemies, but also interesting tropes and situations that may provide some good inspiration for your games.

The Egg has lots of Orcs and humanoids as his followers. Many are based in Ohmfet although he has also likely made alliances with the other Orcs in the North. If you want to stay true to the Mystara continuity, these would be replaced by Beastmen.

As Rob says, Dragons are appropriate. Also constructs and Balrogs (Demons), Vampires and other Undead and Lycantropes.

If you have access to the First Fantasy Camapign, you can take a look at the Egg's roster for the Coot Invasions.

The Egg's forces will often be lead by .

IMC I portray the Egg as a more Cthulhuesque being, so creatures that later editions refer to as Aberrations (Beholders, Nightmare creatures etc) could also be used.

-Havard

Cool, thank you!

Unfortunately I don't have a copy of First Fantasy Campaign.

Thank you all!

We actually just finished this plotline today. I ended up using various undead; humans and half-orcs (both warriors and mages); orcs/gnolls (which the PCs avoided by flying); ogres; wyverns, a behir, and an undead dragon; and finally a beholder as the Egg's "avatar" of sorts.

Was it an overall good experience? :)

Yes, it was quite cool, and went well.

Well... now that you stirred our curiosity, it is just plain good manners to write something about it here: viewforum.php?f=76
...for example....