It stacks additively with your penetration from the upgrade. It meant as a lategame bonus -- it's not really useful until you can easily cap your armor pen upgrade.
neat game, my only tiny little suggestion would be if the turtles became transparent or invisible when you were placing so you can see where you already have mines
i like it but i wish there was a confirmation of some sort when you choose a perk. if you level up in the middle of a firefight it's easy to accidentally take whatever happens to be under your cursor because you didn't realize in time to stop clicking
i think the trick to to the timed levels is to turn around after you kill a pack of them, rather than walking all the way from one side to the other. they seem to prefer to spawn behind you so you will hopefully bump into another group, and repeat.
i like it but some of the achievements seem to be bugged? i can't seem to get bonus kills with the bolt rod, and my tank traps detonated isn't going up. also saw squads are cutting the heads off but then not doing any more damage so i can't get that achievement either.
 "MineQuest"){kind=icon}
 "Arkandian Crusade"){kind=icon}
 "Epic Combo!"){kind=icon}
 "The Final Death Wish"){kind=icon}
 "The Great Massacre"){kind=icon}
 "When The Plague Came"){kind=icon}
 "Puppet Wars"){kind=icon}
It stacks additively with your penetration from the upgrade. It meant as a lategame bonus -- it's not really useful until you can easily cap your armor pen upgrade.