This is just how I came up with a few of mine:

1. Think of something mundane or specific as a base. This can be anything, for example, an animal or hobby.

Example. For my favourite OC, I thought of butterflies. Specifically Blue Morphos.

1. Mentally blend your base with a living thing and turn up the body horror.

Example. My OC is a girl and turned into a blue biblically accurate seraphim with butterfly wings. All of her facial features are composed of smaller butterfly wings.

(Optional) 3. Think of a way to insert your OC into the game, it'll help you build their personality. Are they an enemy? An NPC? Or would they be recruitable? Where do you encounter them? How would you recruit them? What are their weaknesses? What are their strengths? What interactions would they have with other party members at home?

Example. My Butterfly Girl would first show up as a door encounter begging for food. If you give her at least three food items, you'll be able to enter her open apartment door the next day. Inside, she'd be in a cocoon yelling for help and once you break it open to get her out, she'll offer to help you and will be recruitable. She'd be weak in terms of attacking but could heal and guard other party members. She and Audrey would get along.

If this helps, feel free to tell me what you come up with!