Something I've been doing here [link] , drawing various Transformers characters in the Kreon minifigure style (which are basically like Lego minifigs but with better articulation and crappier plastic). You should theoretically be able to make any of these with the existing parts... and some paint and maybe custom decal prints. A few of these --namely Kickback, Bombshell, Rampjet, and the green Rainmaker-- coincidentally ended up getting official Kreons.
I never designed Metroplex with an alt mode in mind.
When I was showing Metroplex to my friend Andrew Hobart I folded open his legs the way you see here and showed him how they were constructed and he said that it looked like I'd made it so Metroplex could Transform. So when I came to take these photos I ripped off Metroplex's arms, his knees, his head and then gave him a city mode. You can see all the pieces that are left over, this guy is definitely a partsformer.
The stickered tile with the city-and-night lights on it, incidentally, is from LEGO. It's from a Star Wars space ship. Man it looked perfect for Metroplex.
Anyway, the reason that the knee caps were even removable, and not a solidly built in part of Metroplex's build (if they had been, he wouldn't have been able to lay down for his alt mode, honestly) was that I always intended for him to have another gimmick. That's right -- I didn't intend him to transform, but I *always* intended him to be able to combine with the Aerialbots.
I'm funny that way.
(For those not in the know, the G1 Metroplex toy is capable of merging with the Aerialbot limbs if you take off his knees and shoulder guns and put the Aerialbots there instead.)
So the entire driving force behind building Metroplex was that I had in my head an idea on how I Could construct his chest so that it would be hollow and you'd be able to fit a little Scamper toy inside there. But it didn't work. The whole thing was a complete goddamn failure.
By that point, though, I'd already partially worked out how to build his legs in my head, so I abandonned the chest and got to work on his legs. The legs completely changed Metroplex's scale -- they were bigger than I expected them to be. That led to reconstructing the chest completely, and now the Scamper gimmick thing works! Woo! Plus you have his revealable chest missile launchers to boot. I'm pretty happy with that.
Here are some shots showing how Metroplex was constructed, his accessories, and other such stuff.
So first up you have his guns and his Scamper. The rifles were designed when I had a different hand design in mind and don't REALLY work with the KRe-O fists I ended up giving him. I'm going to have to slightly redesign them so that instead of handles they'll just clip onto his fists. You'll notice in the second picture that while I haven't built a Sixgun, Metroplex's red rifles were built with that possibility in mind.
Next you have a shot showing how I used Kre-O crotches to give Metroplex his shoulder articulation. This was one of those, "Ahah!" moments after spending a long time during the build thinking I'd just have to give him swivel shoulders.
Finally you can see Metroplex's articulated heel spurs. They were meant to allow him to stand on LEGO studs, but instead actually help him stand on just about any surface OTHER than studs. They're just too small for the final build. I'm going to have to go back and redo them, I just haven't worked out how yet.