Holy Halloween, Batman! The Batman T-Shirt Adult Costume Kit is the best costume for those who want to dress up, but don't want to go all out on October 31. The Batman T-Shirt Adult Costume Kit comes with a cotton Batman T-shirt complete with printed abs and utility belt with an attached flowy cape. To ensure no one uncovers your real identity as a wealthy bachelor, the costume kit also comes with a mask. Get a crew together to dress as the Justice League or villains of Gotham.