Perhaps a villain OC that controls a powerful and corrupted magic. They use this magic to wither the land, turn ponies against each other, and try to take over Equestria. Their origin could be a failed magical experiment long ago.
A shape - shifting villain OC would be really cool. They could disguise themselves as other ponies and cause trouble by spreading false rumors or stealing valuable items. Their true form could be a grotesque and menacing creature.
One idea could be a villain OC who has the power to manipulate dreams. They could enter the ponies' dreams and create nightmares, causing chaos and fear. This villain could be motivated by a desire for power over the dream realm.
A good MLP female OC fanfiction idea could be centered around a female OC that is a hybrid of different pony types. Maybe she's part unicorn, part pegasus and part earth pony. She feels like an outcast in Equestria at first because she doesn't fit into any one group. But as the story progresses, she uses her unique combination of abilities to save Equestria from a new threat. Or perhaps a female OC who is a fashion - forward pony in Canterlot. She starts her own fashion line that combines traditional Equestrian styles with new, edgy looks and has to deal with the cut - throat fashion industry in the city.
One idea could be a male alicorn OC who is an outcast in Equestria because of his unique powers. Maybe he has the ability to control time, which is feared by the other ponies. Another idea is a male alicorn OC who comes from a far - off land and has to adapt to the Equestrian way of life. He could bring new magic or traditions with him. A third idea might be a male alicorn OC who is a detective of sorts, using his magic to solve mysteries in Equestria.
An interesting concept could be a male human OC who is a talented artist. He gets inspired by the colors and beauty of the MLP world and starts creating art that has a magical effect on the ponies. His art could help solve problems in Equestria, like bringing back the lost colors of a fading meadow.
One idea could be to create a villain OC who has the power to manipulate time in small increments. This could lead to really interesting scenarios in battles against the heroes. For example, they could slow down time just enough to dodge attacks and then speed it up suddenly to surprise their opponents.
A third idea is that the male OC is from a different dimension. He accidentally lands in Equestria and meets Sunset Shimmer. At first, Sunset is suspicious of him but realizes he's lost and in need of help. They embark on a journey to find a way to send him back home. Along the way, they encounter various obstacles and have to rely on each other's strengths. This adventure brings them closer together, and by the time they find a way for him to return, they have developed deep feelings for each other.
You could also write a fanfic about an alicorn OC who forms an unlikely friendship with a non - alicorn character. They go on adventures together and learn from each other, facing various challenges in Equestria along the way.
One interesting plot idea could be that the OC is a new kind of magical being that Aria Blaze has never encountered before. Their meeting causes a stir in Equestria as they try to figure out how the OC's magic works and how it could impact the existing magical balance.
A villain OC for a Supergirl fanfiction could be an alien from a dimension where Supergirl is seen as a tyrant. This OC comes to Supergirl's world with the mission to stop her 'tyranny'. The OC could have unique powers like the ability to manipulate time on a small scale. This would create interesting battles between the OC and Supergirl, as Supergirl tries to convince the OC that she is not a tyrant while also dealing with the OC's attacks. The fanfiction could also explore how the people of Supergirl's world react to this new villain who claims to be a liberator.
One interesting MLP OC fanfiction could be about an OC who has the power to control time. The story might explore how this power affects the Equestrian world and the relationships with the main MLP characters. It could be full of adventures as the OC tries to correct mistakes in time.
A villain oc who is a half - human, half - beast hybrid. They were outcast from society because of their appearance and now seek revenge on all the villages. They have unique physical abilities due to their hybrid nature, like super strength and enhanced senses. Or perhaps a villain oc who is a former student of a great ninja but turned against their teachings. They create their own new and dangerous form of ninjutsu that goes against the traditional ways.