Going from the Little Mermaid to Humanoids from the Deep here.

There was a stretch in Avengers when the Beast was a member, and he received significantly less hassle for being a mutant than some: seriously, I think he got less static than his teammate the Scarlet Witch. It may have been because he was approachable, cheery and likable. Not unlike Marrina in today's book, before she went completely monster: from 1986, Alpha Flight #40, "Love" Written by Bill Mantlo, pencils by David Ross, inks by Wilce (Whilce) Portacio.

Along with Puck, Marrina was introduced in Alpha Flight #1, and I wonder how much of this plotline was John Byrne's idea: although I had thought most people assumed she was a mutant, she was actually an alien, of a race called the Plodex. The Plodex's incubator ship should have left eggs enough to overwhelm earth's native life-forms with toothy monsters, except it landed during an ice age and most of the eggs were destroyed. Marrina's egg washed ashore centuries later, where it was found by a fisherman, and she hatched in an amphibious form. Later, the villain called the Master would reveal her origins: he had been a caveman, and not unlike DC's Vandal Savage, received immortality from the Plodex's ship. He also received the last Plodex egg, intended to be her mate.

Except her boyfriend might have something to say about that: none other than Namor, the Sub-Mariner! While Alpha Flight debates the morality of possibly having to kill Marrina, to keep the Plodex from reproducing and spreading monsters across the globe, Namor is willing to fight any and all comers for her. While he could sometimes--often--be a jerk, Namor is surprisingly noble here; especially since being drawn to her Plodex mate has cost Marrina her looks. Still, for Namor, and earth, Marrina renounces her Plodex heritage and genetics; and together with Alpha Flight they tear the mate apart. Finally, with Namor having renounced the throne of Atlantis, its former citizens still loyal accept him as their king, and Marrina as their queen, in their new undersea kingdom of Deluvia. Namor and Marrina are wed, and it's a happy ending...that would last maybe two years.

Marrina had been fortunate enough to be accepted by her adoptive parents, her team, Namor, and Canada at large if I'm not mistaken. If they had been jerks, earth would probably be up to its elbows in Plodex, and they looked pretty terrible. I couldn't say what happened to Deluvia, if it was just absorbed back into Atlantis, or something else; nor do I recall what happened with Namor and Marrina's marriage, since she's come back possibly more than once now. BTW, if you haven't seen Humanoids from the Deep; it's gross. From a sub-genre of rapey monsters...