The 5E Monster Manual gave us a bunch of the most iconic monsters D&D has ever produced. It's like the Hall of Fame for monsters. However, which monsters will be in the next Monster Manual? Which ones do YOU want to see next? For myself...
Oozes (other varities)
Yellow Musk Creeper
Looking through the list of past monsters, there are not a lot of must-haves. The 5E Monster Manual really did a good job at including the "necessary" monsters. From this point on, we'll likely see monster variations (different types of golems, etc), setting specific monsters and the bizarre ones.