Her dad has a point: if you can only form complete half of your body, creating legs, which solves the Mimic specie's inability to walk is a breakthrough in transformation.
Taking your "new" idea to the patent office: It's that thing everyone has done for thousands of years, but you can do it on a computer so it's completely new.
Taking your "new" idea to the copyright office: It's that character the other guy made, but mine has a gun so it's completely new.
You're good little mimic as Sega is nearly the polar opposite of Nintendo when it comes to enforcing copyright. So make your oc do not steal hedgehog adjacent friend with pride.
Taking your "new" idea to the patent office: It's that thing everyone has done for thousands of years, but you can do it on a computer so it's completely new.
Taking your "new" idea to the copyright office: It's that character the other guy made, but mine has a gun so it's completely new.
But if nobody even tries to give protections and incentives to those 'new' ideas you have an arms race of 'the same but better' like we are currently seeing with the likes of Palworld and eventually most people will just stop trying. That would be the worst outcome for everyone.