Dav Pilkey 
Captain Underpants and the Wrath of the Wicked Wedgie Woman [EPUB ebook] 

George and Harold are having a normal kind of week. Yesterday they found out they were going to flunk fourth grade. Today they’ve created an evil, super-powerful monster. She’s mean. She’s got a fake-fur Evil Baddie costume – and she’s having a REALLY bad hair day. With the help of her robots, the Wicked Wedgie Woman is on a mission to take over the world … and she’ll give a whopping wedgie to anyone who stands in her way! Watch out!