Cybertron Form: A Jet-Plane. This gives explanation to why Optimus has built in flight rockets. He had this form before chasing Megatron
and landing on Prehistoric earth.
First Form: Gorilla. This form was chosen by Optimus as a way to prevent energon
build-up on the world he and the other Maximals landed on. Aquring this form gave him some of the animals mannerisms, like a strong sense of smell and swinging through trees. Even though the gorilla is a land based animal, it didn't rid Optimus of his flight rockets from his orginal form.
Transmetal Form: After flying a modified statis-pod to destory an alien device, Optimus's orginal body was destroyed and his spark was lost. But luckily, Rhinox
came across a sparkless protoform and after sending his own spark in space, he found Primal's and had it placed in the protoform. Not only did the Boss Monkey get a new body, but it was a transmetal body. It had three forms: Beast-Mode, Robot-Mode, and Vehicle-Mode. Optimus's Vehicle mode was basically his beast-mode, riding on a jet surf-board.
Optimus gains the ability to reformat robots. And shoots energy discs from his chest. His arms can be used to absorb energy blasts, and shoots them back.