Before anything and everything, I proclaim bring back the XI Mandragoras. They've sort of become a mascot for FF in general thanks to XI. However, I liked a lot of the XII variations on them like Aruane and Deadly Nightshades. So before the Dev team gets into anything, I wanna see them return.

As for some of the nasty beasties we will need to deal with later... First off, I'd like to say we need some abandoned forts to explore. Then get some of the monsters that were exclusively HNMs in XI in as regular monsters, like Khimairas and Behemoths. Personally, for some of the harder dungeons, since I know the AI could handle it, I'd like to see some living statue sort of monsters. They're pretty much still and blend in with other actual statues that look like monsters, but pass to close, and they attack. Also, they should be like Chigoes in XI. Their names don't show and you can't target'em until it's too late. Stuff like Gargoyles and Brain Pans (from XII)

If you're talking about which Behemoth type to use as well, look at XIII. They had both. Once you dealt enough damage to a behemoth, it stood at got mean. So you could have Behemoths that worked like Proto-Omega in XI that switched between stance and which moves it had available. And weather it was weak to magic or physical attacks.

Now, about the time they get around to adding Flayer (if you've ever seen the unofficially leaked list of planned classes, it's the whip class) I'd like to see Lamia return. I think XIV can stand to make them a bit more gorgon like with longer tails than XI did.

Something that feels like it belongs in Mor Dhona... Slaven from XII. Particularly the ones with crystals on their back.

Oh, right. We also need Mech Beats. Like a lot of Machina from X. I figure when we get to the empire areas, we'll see War Mechs and some other robots.