Micro Fiend is a fiend created by A Boy to study cells. Micro Fiend is the size of a small poppy seed and looks like a purple walking rat. It can bring anyone down to it's size which is just big enough for cells to look like small bugs. After A Boy used it, he released it because of it's kind heart. After wandering the streets alone, it was found by A Girl and she adopted it. In season 2, it is een that he is being used to help A Boy & the gang spy on AOS.