If you find it hard to kill the boss at zone 2, get the captain low and he will stun himself for 15 turns, then you can kill the sniper and the medic. Worked for me :).
Really nice game, you can see that the developer put time and effort in it.
I will give you 5/5. I really like it and we need more games like this, it took me a really much time to find this game though...
Dude , the fly train it's OP because i spend just a minute and max my flying ability , but at the end , the climbing and swimming it's hard dude , do something....