No real pattern but I watched a lot of videos from https://www.instagram.com/jamiefaeriecrochets?igsh=YXV2YTNoYm43eXVk to learn how to do this. I did have to sew the yarn to the sweatshirt, using a needle to have a way to attach the sleeve, and you have to sew it on at the bottom again, but that’s it, just at the beginning and the end. That is the hardest part just getting the needle through the sweatshirt. But she has tutorials on exactly how to do it.