Bro tip: When upgrading towers, make them dual machine gun, the cannons are too slow, and the missiles even more, and the idea is avoid the enemies get past the line, and just buy mines and grenade launchers for explosive power against Bosses :)
Ah, and of course, when defending, follow this pattern:
Dogs-->Mutants-->tank guy-->Others
Ok, in the FIRST BOSS (the purple one) You CAN'T GET BACK to surface because the rock resets to it's previous position and the lock closes the way.
Either make 1way door for back, or removing or at least keeping that open.
 "Mini Attack: Urban Combat"){kind=icon}
 "Decision"){kind=icon}
 "Decision 2"){kind=icon}
 "Stable Boy"){kind=icon}
 "Seedling"){kind=icon}
 "Utopian Mining"){kind=icon}
Coming soon!