The Overtank is a massive tank, as the last stage in the growth gamemode. They are slow, but have 6 normal barrels, 6 gunner barrels, and three overseer barrels, each which spawn two (instead of one) triangles at a time. It can hold 12 "doritos". They are probably the best bet in destroying Entropy, the boss in the game.
They can not attack any tanks except for other Overtanks, to keep it fair.