yep, between your 5 books we got dragons, wyrms, and wyverns covered
I guess at this point I am looking for more humanoid variants (goblin, kobold, orc, troll, hobgoblin, sahuagin, kua-toa, lizardmen, …) to mix things up. Some of those might be off limits outside the DMsGuild though… will there be an MME4 at some point?
Yes, there will be an MME4 eventually, but it may not be what you're expecting.
Recently, I ran a poll on my Patreon asking if I should start shifting to a pseudo-version of the new stat block style from MM 2025, and the feedback was interesting. Turns out, 60% of you still prefer the 2014 format, with another 15% still favoring the Legendary Actions + Lair Actions style.
With that in mind, I'm considering sticking to the 2014 stat blocks for Deadly Denizens, then doing MME4 by using art from Deadly Denizens I and II and fresh art (for creatures I couldn't do using OGL) with the 2025-style stat blocks. MME4 will focus mostly on creatures I couldn't touch outside of DM's Guild, but will also include 2025 versions of DD creatures. This approach lets me target both markets without investing heavily in new art. If all goes well, MME4 might hit early 2026… or even late 2025. Maybe!