Villain OCs in that world need a hook that feels rooted in its logic. A common pitfall is just making someone overpowered and edgy. The ones that stick with me have a design that suggests a twisted version of a hero's principles. I saw an OC once whose power was 'Empathy' – not feeling others' emotions, but forcibly imposing their own emotional state on people. Their design was deceptively plain, almost like a tired office worker, but their Quirk manifesting as this oppressive, invisible aura made them terrifying. The costume wasn't leather and spikes; it was a neat, worn-out suit, symbolizing how their villainy wasn't a rebellion but a systemic, soul-crushing pressure. It felt more insidious than any monster.
Another angle is the failed experiment. Tying a design to the established lore, like a byproduct of All For One's machinations or a botched Quirk-suppressant drug trial, adds instant depth. Visuals could include synthetic-looking skin, mismatched limbs that don't seem to belong to the same body, or tech-augmented parts visibly malfunctioning. Their motive often writes itself – rage at the system that created and discarded them. The design tells the story before a single line of dialogue.
Honestly, I'm less impressed by the 'cool factor' and more by the narrative cohesion. A villain whose appearance and ability directly conflict is also strong. Imagine someone with a beautifully elegant, angelic design whose Quirk is something visceral and degrading, like controlling decay or parasites. The dissonance there is a goldmine for unsettling readers and creating a memorable foil for the bright, aspirational heroes.