Long story short, Tenguman decided to "upgrade" everyone. Aside from the fact that Transmetal Tenguman is an homage to King J-Der from GaoGaiGar, this form of Tenguman has a different set of abilities and attacks that are different from his original form. For starters, he has built-in generative armor, which allows him to adjust his speed, offense, and defense for a variety of combat strategys. Second, he has his own J-Quath(which is effectively a boomerang, except is set on fire, and launched from a crossbow. Just go with it) that can be fired at high speeds in order to ensure maximum destruction of his desired target. Add to it, the wings that are folded up from his transformation, can be used like swords to cut through any large objects. Another one of Transmetal Tenguman's abilitys, is his "ES Window"(Short for Escape Window), which lets him create a portal in which he can either travel long distances in a short amount of time, or be used to escape incoming enemy attacks. But due to the fact this move requires a lot of energy to pull off, it takes a while before it can be used again.
The White Battleship
"White Battleship" is the term Tenguman dubbed his vehicle mode in this form. Its basically your typical spaceship, except is what Transmetal Tenguman can transform into. Its main attack method are its dual cannons that can fire at a very fast rate. Also, due to its's placement during transformation, the J-Quath can also be fired at enemies while Transmetal Tenguman is in his vehicle mode. It should be noted, that this vehicle mode is rather flimsy, as it was built for speed. Meaning if Transmetal Tenguman wishes to engage in serious combat, it pretty much forces him to transform.