Yes, I know it's August, but Christmas is always in season....just go to any craft store right now and you will see. ;o) I saw a onsie kind of like this a few years ago. If you have a Cricut or some sort of cutting machine, you can use a reindeer die cut, but you can also just print off a reindeer outline online and use it to cut the shape out of iron on vinyl the old fashion way....scissors.
I found this vinyl with sparkles at Hobby Lobby. I used a coupon, so it was about 8 dollars for four sheets, which is more than I usually would spent, BUT....I can get two deer out of it, and then I'll definitely find a use for the other pieces.
I cut out the shape of the deer, and used the shape to cut out a circle for the nose.
You put it on your shirt/onsie and then put a towel over it and press down with a heated iron to adhere it.