Tank's appearance is modeled after an actual army tank with his left arm resembling a cannon, and his base being like the treads on an army tank as well. Its' appearance also seems to be more metallic and robotic, despite the fact that Robert was carving a wooden puppet for a majority of the film, and it is never explained why Tank seems to have this appearance and not the apperance of a wooden puppet. Tank contains the soul of its namesake, Robert Winsley after he is killed by Dr. Magrew.
The only major difference between an army tank and the Tank puppet is that it has a virtual display unit on the top of its body, which displays Robert's face on it.
Tank's powers seem to resemble Decapitron's powers from Puppet Master 4 and 5, in the fact that it can project lightning-like currents, but it projects it out of its cannon arm rather than its head like Decapitron.
Also like Decapitron, Tank isn't activated by having the formula injected directly into him, but rather seems to be activated the minute Robert's soul is entered into him.
At the end of the film, Tank turns on its creator just like the other puppets (who turned on Dr. Magrew because he killed Robert), and projects a lightning beam between Dr. Magrew's eyes, killing him shortly before the credits roll.