The only problem for me is I can't continue playing because the upkeep for all 5 unique characters are too high and I bankrupt before getting all of them to level 5...
Holding mouse click should be charge attack.
Need more upgrade as a skilltree like attack power, pet support, bomb, edge climbing, etc.
And make a sequel where the main character is a girl. Girl+Tentacle is much better if u know what i mean :)
The best way to level up your guns fast is to let them get damaged. Put them far front, move them just in front of the Red Sploders. I level up my lightbringer from 1 to 7 with only 2 runs in Colossus map.
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He had to fight off the bad guy with his tentacles. =)