Dav Pilkey 
Uranium Unicorns from Uranus [EPUB ebook] 

From the creator of CAPTAIN UNDERPANTS, comes an out-of-this-world friendship adventure – now in full colour. Ricky Ricotta loves his Mighty Robot, but sometimes it’s hard for a little mouse to have a best friend who’s so BIG. One night, Ricky makes a wish: if only his Mighty Robot had another friend who was his own size so he wouldn’t have to hang out with Ricky all the time. Little does Ricky know, his wish is about to come true. Evil Uncle Unicorn has travelled all the way from Uranus with a mean and nasty plan. He’s built a giant Ladybot to trick the Mighty Robot so he can take over planet Earth. Once again, it’s up to Ricky and his pals to save the day.