To play this mod, you need a Custom Campaign Manager.
Here is tutorial made by Giant Grant Games:
https://youtu.be/a_m-ftMVY9g?t=499
--------------------------------------
What are exact changes?
For example, firebats don't have to "channel" their attack, have slightly increased damage and can attack while moving.
or
Diamondbacks deal more damage, have longer reload time and are cheaper.
and many more.