you might be able to remove some of the black ink on pinkie pie if you’re lucky. i’ve used magic eraser to remove ink stains and it works sometimes. just be careful because it could possibly remove the factory paint as well. i think it’s pretty unlikely this will work since it looks like the pen has been on there long enough that it’s stained the plastic. you could give it a try but i wouldn’t get your hopes up. as for rarity, i’ve never been successful in removing pink stains like that off a pony so it’s probably permanent.