Also, this is the SRD - the "genericized" version of the rules, that includes all the core game systems but omits content and references to official lore. (e.g. the SRD has a spell called "Mage’s Private Sanctum", which is mechanically the same as the main ruleset's "Mordenkainen's Private Sanctum".)
beholder, gauth, carrion crawler, tanar’ri, baatezu, displacer beast, githyanki, githzerai, mind flayer, illithid, umber hulk, yuan-ti
If I understand correctly, they only own copyrights for the lore, not the names and appearance. Also product identity so they can't be used by other tabletops, but other media can use them. For example, the game Demon's Souls have Mind Flayers, they are called Mind Flayers and look the part. I doubt From Soft and/or Sony are paying royalties for such minor enemy.
I think this case is different from the Beholder which seemingly they own complete rights since they made Tibia change their Beholder to something distinct.
Tanar'ri and baatezu are, even within full-copyright Official D&D materials, better known as "demons" and "devils", and I have a hard time imagining that any third-party material would want to use the protected names.
Beholders are iconic, and distinctive to D&D, and gauths are derivative of them. There are several other beholder-lites; why aren't spectators protected?
Illithids and mind flayers are the same thing, always fairly iconic and more so now that Baldur's Gate 3 is devoted to them, and githyanki and githzerai are part of the lore developed around them.
Yuan-ti are snake people. They're not distinctive at all; the film Conan the Barbarian has a villain who does a ritual to turn into a giant snake. The general concepts of snake people, snakier people, and evil snake gods are too popular and generic to be protected, but I guess you should call them something other than "yuan-ti".
(Fun side note: the name "yuan-ti" looks like it's obviously Chinese. You can find questions about this all over the Chinese internet, since there's no obvious way to assign meaning to the name. The answer appears to be that the guy who made up the name knew nothing about Chinese and it's all a big coincidence.)
Umber hulks are large insectoid creatures that burrow underground. I'm not sure why they're considered so important, but they're more distinctive than carrion crawlers.
What's more interesting to me is that they're going to review the older edition SRDs, with an aim to releasing those under Creative Commons too, after SRD 5.2 is out.
Positive news.
And when they sent Pinkertons to intimidate someone at their home after they leaked an unreleased card set.
https://www.dicebreaker.com/categories/trading-card-game/new...
So the underlying rules are fine, but having monsters like mindflayers, spells like "magic missile" or "melf's acid arrow", locations like Baldurs Gade, Waterdeep etc are all verboten.
Bit murky with Wizards of the Coast buying TSR and making Baldur's Gate Magic sets.
If it's not generic, was Wizards of the Coast stealing from TSR when it used D&D's Counterspell as the name of a Magic card? Before buying TSR, to be clear.
"Fireball" should be generic. Plenty of prior art on those, I should think.
Kidding, a little bit.