That hideous skull really brings the room together, J'onn.

This issue had kind of a striking cover, and I also didn't remember J'onn had a solo book for so long: from 2001, Martian Manhunter #32, "Bloodworms of Mars!" Story and art and cover by Tom Mandrake.

As detective John Jones, J'onn helps out an old friend with a crime scene investigation: four murders, with acid, and a giant tunnel dug out of the street...actually, the weird thing is, they're treating that like a crime scene and haven't called in the National Guard! Changing form, J'onn investigates, following the tunnel and finding a long-abandoned White Martian base. He finds evidence that they were experimenting, with the dread "B'ool Sporath," the Bloodworms of Mars! A scourge that dissolved White and Green Martian alike, to drink the remains; a menace so horrible the two races had put aside their ancient grudges to defeat them. Some White Martians saved some, probably to use in later atrocities, but either lost them, or were able to wipe out the Greens without them.

J'onn realizes while Martians had been completely dissolved by the Bloodworms, humans were merely skeletonized; so he forms a bony exoskeleton armor to protect himself while he carries the worms into low orbit, where they would burn up on re-entry. He then finds a single Bloodworm egg remaining, and can't bring himself to wipe out a species, so he puts it in his secret base, along with the remains of the others, reminding himself he was "a creature of the red sands," a Martian even if earth was his home.

Of course J'onn finds White Martian stuff: if it had been Kryptonian or Thanagarian or something, it would've been somebody else's problem! This was Mandrake's last issue, although he would still do some covers; but only four issues remained. That would be almost a Martian Manhunter: Year One story, "In My Life," set while he lived on Mars and fought Apokolips...!