In Elden Ring, one of the bosses that you can encounter is a ogreish warrior known as Margit the Fell Omen, which in Japanese corresponds to: 忌み鬼マルギット (Imi Oni Marugitto, "Shunned Oni Margit").

Oni here doesn't literally refer to the mythical creature itself, but moreover to the idea of Margit being shunned because of his monstrous appearance. "Fell" reappears throughout Elden Ring as a consistent localisation choice for 忌み (imi, "shunned, prohibited, taboo"), derived from the verb 忌む (imu, "to detest"). Related is also the adjective 忌々しい (imaimashii, "provoking, annoying"). All in all this suggests that Margit was not just unwanted, but thoroughly reviled because of his horned looks - which bode ill in the mythology of the game.

Fell in English is an archaic word meaning "ruthless, savage" (derived from Middle English fell ("angry, fierce"), and in general describes something monstrous or ill-boding:

But my heart forbodes that, ere all is ended, you, Frodo son of Drogo, will know more of these fell things than Gildor Inglorion.
(Lord of the Rings - Fellowship of the Ring, Tolkien)

"Fell things" here referring to the hordes of Mordor, warped and cursed beings that all serve the eponymous Lord of the Rings, Sauron.