Cyberfire and Brimstone
Transformation was pretty simple, but still pretty unique. A simple rearranging of parts and his legs formed the pterodactyl's head while his arms formed it's feet. In beast mode Brimstone was pretty solid thanks to his simple transformation. Simple doesn't mean bad though as the toy looked great in both modes and didn't sacrifice anything in the process.
Oddly enough Brimstone's mold was a 'one and done' that rarely happens in Transformers. I blame timing as the toy didn't really fit in with following lines while other Cybertron toy molds got folded into various reuses. Aside from his Japanese counterpart and random value pack style releases there just wasn't any other use of the toy mold. Which is a shame as I can easily see him as a Windstorm homage. Fortunately he did get some love later as the character returned as a BotCon exclusive.