In the 5.1 SRD that just got released into the Creative Commons is a bunch of IP including Count Strahd von Zarovich, the Feywild, the Shadowfell, the City of Brass, Palace of Dispater, Street of Steel, Gate of Ashes, and the Sea of Fire. The beholder is also specifically referenced by name in the Deck of Illusions, and Mind Flayers and Slaad are also referenced--at least by name--repeatedly in the document.
Here's a link to the content released to CC.
WotC Backs Down: Original OGL To Be Left Untouched; Whole 5E Rules Released as Creative Commons
Hundreds of game publishers sigh in relief as, after extensive pressure exerted by the entire open gaming community, WotC has agreed to leave the original Open Gaming License untouched and put the whole of the 5E rules into Creative Commons. So, what's happened? The Open Gaming Licence v1.0a...
www.enworld.org
What does that mean? Under OGL v1.0a terms like this were generally designated as ‘Product Identity’ and were unavailable for use. The CC license has no such provision. This means that those using the OGL cannot (still) use terms designated as PI, but those using the CC can use the full content of the document released under it.
Only the names of these creatures and places are contained in the document--so you can't use Strahd's image or stat block or description, nor can you use those of the beholder, etc. But it does appear that you can refer to these items.
