The Thunderinions: Evil's Rise by Josie Campbell

When five students graduate high school, Glory, Ray, Misty, Phoenix and Forrest, Glory starts experiencing some strange visions. They soon realize that their old imaginary friends are really magical creatures called Thunderinions and that there are five Thunderinion mothers who were captured and are being held captive by the Evil Thunderinions. The leader of the Evil Thunderinions has poisoned the five, but they have no cure apart from the mother. They know what they must do, but how will they figure out where their mothers are being kept.