Unsuck Heroes is a series about making characters who suck not suck, as explained here:
I’ve always liked the Martian Manhunter. Superman is what happens with an extrovert starting over blissfully unaware he’s the last of his kind; Manhunter is an introvert who witnessed his people’s last gasp and knows what he lost. He’s an empath whose whole existence has been a trauma, but he’s still trying to make the world better… even as he struggles to truly be a part of it. But I’m also not making the argument that he doesn’t suck. He does, most of the time, despite all of this potential.
1) Calling him the ‘Martian Manhunter’ makes as much sense as calling Superman the ‘Kryptonian Plumber.’ Sure, he’s probably fixed a toilet or two in his day, but that’s… really not what he does. So we fix that by making John… a manhunter by trade. At one point, the Oan Manhunters reached as far as Mars. While the Manhunters were marginally in charge of the sector, the Oans had discovered they lacked social graces, and sometimes partnering with locals meant that they could more easily handle cases requiring nuance and tact. Depending on the timeline, John can either be one of these who partnered with the Manhunters, or just someone brought up in the same traditions- that all sort of hinges on how old you want your Green Lantern Corps. to be. John was on one of these manhunting missions off-world, on Earth, actually, when the Martian cataclysm occurred. He returned, to try to help, but was powerless to stop it, and forced to watch his family’s demise. He tracked the origins of the cataclysm back to Earth, where an unethical scientist accidentally created the psychic virus that killed every other Martian. John wonders if he’s immune, which brings the horrifying realization that he might have been the carrier that transmitted the virus home.
2) Because he’s a second-stringer, he’s always being sidelined for Superman. But some of this inevitably comes from the fact that he’s been a second-stringer, and therefore never got his own rogues, which leads to a spiral- no archnemesis of note means no starring role and down and down we go. This is helped by the backstory in 1. That unethical scientist is a Luthor type. But unlike Lex, having his own resources to fall back on, he’s a con man- smart enough to fleece people to fund his research, and then disappear before the check comes due. This also makes it necessary for John to hunt for him- especially since his first invention upon meeting John was a helmet that shields him from John’s telepathy.
3) Fire bad. Okay… this one’s going to be a bumpy ride. Because the thing is, the one thing guaranteed to be at literally every superhero fight, is fire. He might as well be vulnerable to oxygen. But… I have a solve- courtesy of Batman. Wayne was working on new heat-absorbing panels for a next-gen shuttle; they’re meant to function like scale armor, or a phalanx’s shields, interlocking in such a way to minimize heat leakage between them. John essentially carries some of these in his body at all times, and can assemble them in such a way that he can make himself somewhat fireproof; he can’t phase them, and holding them in place would essentially require all his shapeshifting concentration, so they would greatly reduce his ability to move or pass through matter, but it means that he can at least withstand some fire temporarily. It’s not a complete fix… but honestly, I wouldn’t want one. John’s already the Superman problem times 20- he has a superpower for literally every situation and only the one, largely silly vulnerability. We have to give the villains at least a little bit of a chance.
4) Personality-wise, though… John sucks. This is honestly probably where he sucks the absolute most. Because his entire character is essentially locked in as a perpetual outsider. It’s lazy, and worse, nonsensical. He’s a telepath, skilled at manhunting, which involves at least some ability to blend into a native population. Sure, at some core level, he’d struggle as one of the last Martians. But he can read minds, he’s empathic even when he’s being portrayed as cold. I think this calls for a whole arc, frankly. John starts pissed at being alone, the last of his kind. He hunts down the scientist responsible for his specie’s near-extinction… but along the way realizes how many people are just as vulnerable and deserving of care and protection as his family. John goes from wanting to burn the world and the entire species responsible for his loss, to wanting to hold the scientist responsible according to the Earth’s laws, while working to help humanity embrace its better nature, and his own.