I'm kinda late on this topic, but nobody seems to have answered this point. Are you getting at what the intelligent design behind the third mode was?

I wondered that myself and would appreciate anyone answering even if it's speculation.

 

The two factions in the begining had their bodies adapted to the environment and designed for disguise among the local wildlife. I'll also accept that an energy wave would remake SOME of their bodies into Transmetals. What I don't get is why Rattrap would have wheels, or Primal a surf board. Or even why Tarantulas would form a motorcycle. There's no real explanation for it. Anyone have a good answer?

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I think madman's answer is as good as any. They never explain it at all in the TV show.

If I had to guess I'd say that perhaps the energy wave triggered something within them that caused them to partially revert to their former vehicle mode (that's assuming that at one time they were tf's with a vehicle mode) leaving them as a kind of hybrid of the two.

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That's a really good explanation :clap

Gives a little background on each character if it's true.