Game's been updated! It's nothing much, but I'll give you the rundown on progression:
A) In the beginning, the only monsters that can spawn are zombies, and they're hella slow
B) A zombie's speed gradually increases whenever a player kills a monster. It's small enough to be unnoticeable at a small scale, but once the player has killed like 40 monsters, their speed is noticeably higher.
C) Another monster has been added: the troll. The troll will sprint at you and does a lot of damage, but goes down in two hits. This will only spawn once the player has made quite a bit of progress
D) The Green and Gold potions (Max Mana increase and Max Health Increase) can only spawn if the player is actively hunting enemies, as to make a better difficulty curve.