Party City adds customization!
The ability to have custom printed party goods has long been wanted by parents of Sonic fans, & PC now grants the ability with a birthday banner, as well as invitations and thank-you cards. The banner has waving Tails on one side & thumb-forward Sonic on the other. The name & year can be anything you want.
The invitations have Sonic Tails & Knuckles on one side, with Sonic on the other. Not only can the name be added, along with the dates/times/address, but you can have a portrait (or a picture of anything) in one of the rings. Their slogan is "so speed on over to the party"

The thank-you cards have the slogan "Thanks for running on over!" along with jumping punch Sonic & punching Knuckles. You can customize these too, but it's not real clear what you'd customize there. These are both sold as packs of 8.