Dragons can be bipedal, quadrupedal, winged, have necks of various size, and have heads or tails in ranging numbers. Indeed, since the term "dragon" is so generic, it seems possible to describe creatures not native to Earth which fall under the very forgiving criteria as dragons.
Generation One animated continuity
At least one full-on dragon (reptilian, fire-breathing, winged) has been seen on Earth in medieval times, and a similar but less imposing creature (supposedly from Borneo) in the modern era. The medieval dragon was tremendous in size, dwarfing both humans and averaged-sized Transformers. Although quite dangerous, it was driven off by a wizard using dragon's bane.
Lord Chumley spent years patiently stalking the Kinabalu dragon of Borneo before transporting it back to his estate. He later set it against the captive Optimus Prime. Kinabalu was a little larger than Prime, had no wings, and did not breathe fire. It attacked him with teeth and claws, but Prime threw it off a bridge.
Also, the fictional movie monster Hojoni bears a striking resemblance to the medieval dragon, though wingless.
Beast Wars II
Galvatron had the computer on Gaea (future Earth) download the most powerful creature from the planet's past, which resulted in the DNA of a dragon being downloaded into his system along with the planet's most powerful weapon, which turned out to be a drill tank for some odd reason.
Cryotek attempted to remove Megatron's Transmetal II dragon mode and incorporate it into himself, but the process left Cyotek into stasis lock. Megatron's beast mode wasn't removed, but Cryotek was left with a similar body.
Robots in Disguise
Among the various forms used by the six-changer Predacon Leader Megatron, a two-headed dragon was one of his more well-known (and more creative) forms. Later, after his conversion into the more powerful "ten-changer" Galvatron, he gained a second (one-headed) dragon form. (This was originally a pteranodon in Car Robots, but was changed for the US release.)
The leader of Jungle Planet, Scourge, transformed into a mechanical dragon with the ability to deploy up to three heads. Though the Jungle Planet is populated entirely by Transformers who transform into mechanical beast modes seemingly modeled after Earth creatures, it is unknown if Scourge's alt-mode has any direct connection to mythological dragons of Earth, which he expressed confusion about.
An ancient race of Cybertronian reptiles known as Predacons resemble dragons. The first of them was cloned back from extinction by Shockwave, as a way of combating the remaining Autobot forces on earth. Also, Wreckers do not know what a dragon is.
- ↑ The Kinabalu dragon was not named, but details specific to its myth were alluded to