Here's some preview art from the 2025 Monster Manual, courtesy of Wizards of the Coast's "Everything You Need to Know Video" on the new book. 
A classic Faceless Stalker:
		
		
	
	
		
	
A demon of some kind:
		
	
Arch-Hags:
		
	
Some kobolds:
		
	
A Nalfeshnee, perhaps?
		
	
A revenant:
		
	
Blue dracolich:
		
	
Death Knight:
		
	
Death tyrant:
		
	
Chimera:
		
	
Githyanki (with the central warrior recreating a classic pose):
		
	
A mummy lord:
		
	
A marrow:
		
	
Abalrog balor:
		
	
Mimics:
		
	
While I'm tempted to say a tressym, this actually might be a new sphinx design:
		
	
Bone fiend:
		
	
Sladd:
		
	
Rust monster:
		
	
Platinum(?) dragon:
		
	
Bronze dragon:
		
	
Hezrou, perhaps?
		
	
Fire giant, not Karlach:
		
	
Cloud giants:
		
	
Zombies:
		
	
Red dragon:
		
	
Hags (including a male hag):
		
	
Dryads (including a male dryad):
		
	
Horned devil:
		
	
Incubus and succubus:
		
	
Vampires:
		
	
		
	
Vampire:
		
	
Colossus:
		
	
Spirit naga:
		
	
Copper dragon:
		
	
White dragon:
		
	
Blue dragon:
		
	
Gold dragon:
		
	
Black dragon:
		
	
				
			A classic Faceless Stalker:
A demon of some kind:
Arch-Hags:
Some kobolds:
A Nalfeshnee, perhaps?
A revenant:
Blue dracolich:
Death Knight:
Death tyrant:
Chimera:
Githyanki (with the central warrior recreating a classic pose):
A mummy lord:
A marrow:
A
Mimics:
While I'm tempted to say a tressym, this actually might be a new sphinx design:
Bone fiend:
Sladd:
Rust monster:
Platinum(?) dragon:
Bronze dragon:
Hezrou, perhaps?
Fire giant, not Karlach:
Cloud giants:
Zombies:
Red dragon:
Hags (including a male hag):
Dryads (including a male dryad):
Horned devil:
Incubus and succubus:
Vampires:
Vampire:
Colossus:
Spirit naga:
Copper dragon:
White dragon:
Blue dragon:
Gold dragon:
Black dragon:
				
					