Rather than going through an listing every creature from the original MM, FF, and MM2 that is represented in the upcoming Adventures Dark and Deep™ Bestiary, I thought it might be illustrative to list the beasties that aren't to be found in it:
Adherer, Aleax, Astral Searcher, Berbalang, Carbuncle, Cifal, Clubneck (but there are three other kinds of giant walking birds to make up for it), Crypt Thing, Denzelian, Disenchanter, Oriental Dragons (to be included in a forthcoming supplement on Wuxia-type adventures), Enveloper, Eye of Fear and Flame, Frost Man, Gambado, Garbug, Giant Strider, Gorbel, Hook Horror, Hound of Ill Omen, Imorph, Kamdan, Killmoulis, Lava Children, Magnesium Spirit, Meenlock, Needleman, Pĕnanggalan, Protein Polymorph, Sandman, Sheet Ghoul, Sheet Phantom, Shocker, Skulk, Terithran, Tiger Fly, Tirapheg, Trilloch, Ice Troll, Spirit Troll, Tween, Umpleby, Vision, Vortex, Witherstench, and Xill.
Aside from possibly an odd dinosaur or two, everything else from the original three monster books is going to be found in the Bestiary (or at least something that can be used in lieu of those creatures which cannot be included due to their not having been declared Open Game Content). We're talking over 900 creatures, including nearly a hundred new ones.
Most of the omissions were made simply because I find the particular creature either useless, goofy, unnecessarily complicated, or a combination thereof. I'm sure some people are going to be unhappy at some of my specific choices (I await the torrent of comments from fans of the Protein Polymorph with both dread and anticipation), but without specific guidance from Gygax as to which creatures, exactly, he was planning on excising from his 2nd edition, I had to go with my own judgement.
However, I didn't have the heart to take out the flumph. That's in there.
The Kickstarter to fund the artwork for the Bestiary will be starting up sometime in May. Keep an eye out!