#ectoplasm

In Transformers prime there’s an episode where Starscream infuses his energon into a bunch of empty protoforms on the Harbinger. Those protoforms could absorb CNA in order to create a clone of the original person, even with just a single vial of Energon. 

Since ectoplasm and energon are so similar, if Danny were to try and overshadow one of these protoforms, it could copy his DNA instead and give him his own Cybertronian form. Danny could either house his consciousness inside it, or his core itself could reside where the spark would normally be.

This would especially be better for Danny as his human body gets older, especially with the ghost portals closed he wont be getting enough energy. So a cybertronian form could make a perfect host for his soul.

I also like to imagine that ghost Danny could function like a holo-form, appearing outside of the mech body when he wants—almost like a physical projection.

Danny would absolutely be a natural flyer. I keep imagining a scenario where Starscream, Breakdown, and Knockout are all trying to teach him how to use his Cybertronian body, and he just… gets it immediately. He’d totally challenge Knockout to a race, and Knockout would lose and say Danny was cheating because his wheels don’t even touch the ground.

Breakdown would try to train him in Cybertronian combat, and Danny would win... like instantly because he’s been fighting things bigger than Breakdown since he was fourteen.

Danny would be awful at landings, though (I think that part is universal).

I also had the idea that, kind of like Mirage in the newer live-action movie, Danny could create multiple versions of himself through duplication. They would be green semi-hardlight holograms, ectoplasmic projections that can interact a little but are mostly meant for distraction and confusion.

For weapons, I imagine something similar to Megatron’s blade that retracts into his arm: Danny would have a glowing green sword made out of ectoplasmic energy that cut through dimensions the same way his claws can. 

He could use it to essentially teleport short distances during battle. Other than that, he would have his servo convert into an ectoblaster. I might also give him a welder like Ratchet’s so he can help out in the medbay. He would absolutely use intangibility there, too! He could phase into frames to remove damaged components. His invisibility and other ghost abilities would carry over as well, just expressed in a Cybertronian frame that makes it look like it is built in.  Naturally, everyone would be horrified and impressed.

I also like the idea that the scars Danny carries in his ghost form would transfer to his Cybertronian body. Likely on the protoform! The first time KO or Ratchet check it out, they are horrified. Especially because Danny's frame would be closer equivalent to Bumblebee's age.

At one point (this idea was from before Falling Stars), I imagined the Autobots running into Danny after he helps save one of them. They’re shocked because, from their perspective, there’s suddenly a brand-new Seeker (or something close to one) fighting for the Decepticons. They don't know how he got there.

In fights, I imagine Danny actively protecting Vehicons from Autobots and getting genuinely upset with them. The Autobots would be completely gobsmacked by how powerful he is.

Also, with Danny's green optics (also this being set after the synth-en Episode where Ratchet loses a sample of the synthetic energy to the Decepticons), they would be worried that Megatron or maybe the Decepticons as a whole had built Danny using synth-en to be some kind of Cybertronian superweapon. Because of this, they would likely try to "rescue" him.

Danny is also great with the human kids... and can use his holo form around them as well when they are hanging out. The kids would complain that the Autobots don't use holo forms and Ratchets just over here staring at Danny's ghost form outside his Cybertronian body in shock because there is a spark in that too!