While I was looking up analysis online of the various played out tropes indulged in during creators' usage of the crappy Batman villain Hush (short version: all of them,) I found an old post at The Absorbascon blog under the heading The Conceptual Hall of Shame. The subtitle was "The Vengeful Childhood Friend," and I assume it was intended to be part of a series. I actually posted a comment back when it was published, but I don't recall if the series was ever continued, and the blog has a horrendous archival system.
Anyway, the thrust of the post was noting that it's a lousy idea to retcon a childhood best friend into the cannon of a well established super-hero who then arbitrarily makes a heel turn into super-villainy. From Conduit to Cobalt Blue, the writer implant usually blows up in the project's face and becomes the subject of endless ridicule.
Curiously, though not entire unpredictably, Ma'alefa'ak bucked this trend. Likely due to the reading public's lack of knowledge about the Martian Manhunter's publishing history, John Ostrander and Tom Mandrake managed to check off every "not-to-do" box discussed by Scipio, and it was actually embraced by modern fans, to the point where he became the first true Manhunter rogue to make it into animation.
- Unlikely continued use of diminutive first name from childhood: His villainous name is Malefic, which is just an anglicizing of the Martian Ma'alefa'ak. Most Martians have relatively phonetic versions of Earth names, but the one born evil Martian is christened such by his own mother, and given a bogus translation like "one who turns to darkness." It may not be diminutive, but it is ridiculously on the nose.
- Vague and weak motivation against the hero: Malefic's motivation was that he was crazy and wanted to kill everybody on Mars, and he only got away with it by being J'Onn's brother. While every other Martian was going all Scott Evil on the matter, J'Onn defended his always obviously evil brother because he's just that good, gosh darn it.
- Knowledge of the hero's secret identity or other personal weaknesses: Evil twin brother. Done.
- Vague powers and abilities: Malefic had all the same powers as Martian Manhunter's notoriously ill-defined set, except telepathy, except when it turned out that he did after all.
- Nearly random noun for codename:
I. Having or exerting a malignant influence.
II. Evil; malicious.
- Vague and inconclusive ending to their storyline: Malefic's story ended when he wasn't saved by Superman after Z'Onn Z'Orr was flown into the sun, be he keeps popping up as some psychic artifact/repressed memory thing.
Beat for beat, Malefic is this trope. He even replaced a preexisting younger brother, and made sure to sit through fifty years of Manhunter crime fighting before swinging by the Earth teleportationally (while J'Onn just wandered around waiting to get zapped by Dr. Erdel.)