Good battle system, but a few suggestions I think would be good. Switch the sniper ability and standard targeting. Default should be the enemy directly across, and sniper should focus on lowest HP. If there's no enemy directly across, it'll go for closest.
Also, customized abilities, or a skill tree would be nice for later versions. You could do a point buy system for abilities for standard multiplayer, or a skill tree idea for campaigns.
87 on endless with 2 Shadow Dragons, a Spartan, and Romeo-S. You can switch out a Devourer for the Spartan, and it does about the same (usually a little less). It's a bit random, so you can get a few more or less rounds with this method.
Great game, but the Tesla needs a little love. The Bertha trumps it in basically every way, except anti-air (and it's not particularly bad at that, either). Maybe make the fairly weak abilities cheaper, so that it's at least cheaper than the Bertha fully upgraded by a decent bit.
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yeah that was the idea .. otherwise you'll have too much to hold on to ;)