Shadow Doll is use by Jirara. Jirara will use the body of him/her to attack who he's attacking. In episode 34, season 4 in Sgt. Frog and in episode 189 in Keroro Gunsou he use it on Koyuki-dono. Jirara will be the shadow of him/her and you can see Jirara eyes on the shadow and sometimes the shadow is red. You will have to hit the shadow to make Jirara get out of him/her body.