In 1e MM 248, maedar was a male subrace of the meduse.
In Dragon Magazine #355, maedar were added to the creature catalogue (3.5e).
In 4e MM 187, male meduse are inferior to the female meduse of the matriarchal race due to their weaker gaze abilities.
In 5e MM 214, a medusa is female or male without any difference in statistics (they also use the plural medusas instead of the etymologically correct meduse).
So male meduse are an established part of 5e-lore that are no longer inferior or have statistics different from female meduse. When I search for images of 5e male meduse, I do not find a single WotC published full body depiction of a male medusa.
Marlos Urnrayle is only displayed with a picture of his head (PotA 199).
The only descriptions that the 5e MM 214 offers for a medusa after their transformation is:
serpent-haired
monstrous form and caprice.
and the depiction of a female medusa.
Is that all material that 5e offers for me to make my description of male meduse in the Forgotten Realms?
I am creating an encounter chain that relies on the description of five separately occurring male meduse. The setting is the Forgotten Realms (after the Blue Breath of Change, in 1492 DR if that is relevant). I am fully aware that I can make up the descriptions as I see fit, but I want the description to be as close to canonical as possible.
I am not interested in answers along the lines of "you are the DM make it up." I am interested in incorporating specific lore into my game.
Best Answer
You can find a bit of reference in the article "Villains: Cult of the Black Earth" on the D&D website.
It contains a few images of Marlos Unrayle (a male medusa from the Princes of the Apocalypse adventure), including a full-body one: