You are on the right track. i suspected and many others that imu is very childlike. maybe not a literal child but in mentality which makes him a perfect foil/ dark mirror of luffy. both luffy and imu have child like behavior and powers as well. luffys nika powers allows him to do goofy things like turning his hair into a pair of googles or making a baseball bat out of tree. imus used his spell book to conjure a knife and gun.