I received a pet from a friend that has a custom overlay. Is there any way to clear it from the pet? I've gone to the description and cleared out everything that was there, but my pet still looks like the custom.

If it's been submitted as a custom overlay I think you need to remove it from here

But I didn't submit the overlay. :(

Did your friend though? If it is submitted as a custom overlay and you don't have an option to remove it anywhere on that page you may need to file a ticket and have staff help you.