This guy floats about using a small jet on his underside - he would be just floating and carrying stuff like rocks, smelting pots, hamburgers, etc.
This is a basic crane design, I like the idea of having stuff constantly being poured everywhere. You'll see more of that in a bit.
The idea with this one is that it has a super laser that cuts tough rock. It would be on a cliffside or surface somewhere and would bore holes into stuff. You could change the laser out for a drill too if you want it less distracting I guess. I'm not going to draw that though.
Having a ton of these migrate across the background could look kinda pimp.
K, here's the nasty color attempts. Volcanoes are harrrrrd. This bridge isn't supposed to be the fighting area, just something they pass while traveling around the stage. That's supposed to look like a big lava-fall at the bottom.
This robot guy isn't toally fleshed out, but the idea is you see him wayyy in the background and he's enormous and just spitting lava into molds on a conveyer belt. Then, he notices the traveling platform the fighters are on and he looks over with the creepy glowing eyes. Just as he reaches out to nab them, the platform jerks in a different direction and he disappears from view. Just an idear.