Some ideas for a new MM. Will update as the thread goes.
Animals
Dog (with pet end bonus)
Hyena
Constructs
Animated Construct (with pet end bonus, perhaps animated weapons or book)
Helmed Horror
Elemental
Fire Elemental - Cinderspawn
Giants
Cloud Giant
Fire Giant
Frost Giant
Stone Giant
Monstrous Humanoids
Harpy
Wildmen
Outsiders
Archon
Fire Reaver
Slaad
Player Races
Half Elf
Half Orc
Undead
Ghost
Spectre
Wheep
Wight
Vampire
That's my idea, anyways. Seems like a good amount and some long awaited additions to the MM.
Would like to thank glmfw1, Deadlock, Dabima, and Dreppo for their contributions.