Chthon has all of Mags evil dad stuff amped up to 11 and made creepy, combined with being the all-important arch nemesis (and, in a perfect thematic flow, the father of witchcraft), that every hero needs to be credible. He also connects her to Thor, Blade, and Werewolf by Night.
You also have Set, Lore, and Master Pandemonium. A very strong rogues gallery, probably the best of any Marvel female.
Which makes the incompetent handling of her all the more infuriating.
Same with Janet. A ton of potential but Marvel shits on her, forgetting her qualities as a leader.