More randomized monsters!
I think it'd be a nice idea to make this more random, so that there'll be a wider variety of monsters to encounter.
An example:
Stone Vault 3 has 4 monsters, two new ones, Dodo and Cursie
Stone Vault 4 has 4 monsters, and two new monsters, Antee and Lux
You will however, never encounter monsters like Cursie, Antee or Lux in Stone Vault again.
A wider variety would mean that you'll be able to encounter all the monsters you've encountered so far, so not only in that map.
For instance:
Right now, Stone Vault 9 only has 3 monsters. I would also like to see monsters like Cursie, Lux or Antee in this map!