Okay we all know Martian Manhunter is a powerful character offensively as he even has kryptonians beat in that department.

However defensive, is he that strong? I know his shapeshifting allows him to take impact force pretty good, but what about everything else? It's not exactly a secret Jonn is a character that's pretty easy for writers to take out of a story early. Not just fire, but even various energy attacks and chemicals I don't recall him doing that well against them.

For example I remember in Prometheus's debut story, he shot Jonn with a dart that has some chemical in it, and then Jonn was a puddle throughout the entire story. I also remember Black Adam one shotting Jonn with the Shazam lightning. Granted one can make the magic argument, but I for the life of me can't think of one example of Jonn getting hit by any sort of energy beam and being fine. On that same note, how well does he handle getting stabbed?

J'onn is a frequent victim of the Worf effect, taken down to show how dangerous the opponent is supposed to be.

-J

Well it can always be worse. He can be Marvel's Eternity who I don't think has won a fight on his own since the literal 1960s. I don't know if I should laugh or cry when I saw things like Ancient One knocking out Eternity with a submission hold or Eternity taking a cheap shot at Hank Pym only for Pym to get back up from it.

I'm not even sure why he punched Hank. I reckon Eternity saw a chance to finally have a win in what felt like forever, but couldn't even achieve that.

Just to be clear, the Eternity who took a shot at Hank was not the real Eternity.
It was later revealed to be a disguised Loki.
Or something like that.
(It's been awhile since I read that).

And he doesn’t have the fanboy aura that would protect him from stuff like that. And when you’re an incredibly powerful being who’s almost never the lead, you take plenty of punishment a lead character of similar power wouldn’t.

Or you get sidelined and used as a threat.

“Sure, Superman and Wonder Woman are here. But keep pushing us, and we’ll tell J’onn to get off his monitor duties and come wreck the place.”

Can't he he remain in an intangible state for as long as he pleases? As in, everything that you throw at him passes right through? Other characters can dodge/teleport, but that requires precise timing.

He might be able to, but in execution it's usually mixed. For instance, in Injustice (Elseworld's story, but bear with me) he had gone intangible, then inhabited Wonder Woman's body to control her mentally. Superman responded by hitting Diana with his heat vision, which incinerated J'onn.

Bottom line, I don't think his intangibility works against heat/fire.

Probably depends on the writer. I think I have also seen him maintain intangibility and invisibility simultaneously.

That was pretty great in Final Crisis what Libra said before running him through with a flaming spear—"I'd hate to take this one on in a fair fight!"