Things You'll Need
Black long sleeved shirt
Black tights of pants
Black makeup for nose
Start with a black top. Since Mickey is a black mouse, long sleeves would be best. A cotton pullover would work as well.
Add black tights or pants for the mouse "legs."
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Grab a pair of bright red shorts and pull them over the tights or pants. If you don't have black tights or pants you can simply do the red shorts or wear red pants.
Tie on some yellow shoes. Mickey has big yellow feet, so yellow sneakers that are brightly colored would probably work.
Add white gloves and black mouse ears. Use black eyeliner or costume makeup to blacken your nose to make it appear more mouse-like.