U can buy commanders which u can upgrade (unit shoots faster, further, generates more credits etc. etc.) and u can buy/earn upgrade for the units. (like more damage, bigger radius, change to set on fire etc etc.)
Also u can buy "slots" (with credits) so every time u go in a new battle u have a unit which u can upgrade fast.
The difficulty is a little harder, and in the start it is hard to understand what everything does and what u can do.
The game is completely free, although they want u to buy a lot of shit to speed up the progress! also no idea if u can make it to the end without paying....
>giving in to the horrible business model virtually every mobile game developer applies to ruin poor parents' bank accounts who let their kids play 'games' on their tablet/phone
Honestly the entirety of mobile gaming is one huge, cancerous tumor that ought to be strangled while it's still young and innocent.