I haven't got art of them yet, but I suppose I should share some of my ideas...I'm sure some of these names are already taken, but it's hard to be original when it comes to RMs.
Tex ManA rootin'-tootin' robot modelled after a gunslingin' cowboy from the Wild West. His main weapon is the Tex Gunner, which snipes out nearby enemies and shoots 'em down.
Phantom ManA ghost-like robot with an upper-crust English accent. His weapon is the Phantom Hold, which lets him possess inanimate objects or other robots.
Construct ManFitting the "hulking brute" archetype nicely, he is large and tough in stature and grumpy to boot. His weapon is Construct Wrecker, a hefty wrecking ball.
Flood ManA water-based robot, he has no real physical form, since he is comprised of pieces of metal armour with a torrent of water as his body. His weapon, Flood Whirl, summons a powerful whirlpool to suck in and crush foes.
Cleave ManA wise and masterly robot, he acts like a sagely sensei and wears flowing robes to emphasize this (he removes them for battle, of course). His weapon is Cleave Blade, a large, curved sword that can slice through almost anything.
Marchen GalA cute little witch robot with a fairy tale motif. Her weapon, Marchen Rod, is a staff that allows her control the wind. She can also ride around on it like a flying broom.
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This is the best Robot Master idea I have ever seen.
Well, not really, but it's still hilarious.