Right now the engine supports 10 different unit types per level (5 player controlled and 5 computer controlled). Each one can have a different attack type, attack power and speed. Also, each level has it's own graphics
So a campaign can have many levels with different units in each one.
Units can't level though, but it's possible to change attack type, speed or attack power in a level.
It's the attack type I want to change in the next version, right now it has two different types: ranged or melee. I want to change it into three types instead, which can be defined by the level creator. So that the ranged units don't have larger range on the map but instead might be more powerful against another weapon/attack type. This will not be in the beta though since that level is already complete.
I will also include the source file (xml) to the level so you may check it if you want to see how the level was created (more information about level creation later
Edit:
My level compiler still hates me :/ So I made it output binaries instead of .83p/.8xp files and used wabbitsign instead... The files should hopefully work fine when I upload them tomorrow...