Witch's Dog and the Crystal Ball

Wilf, the Witch's Dog, is full of magic ideas that help Weenie to think of something to make for the Witches' Fun Day. But in the sports, disaster strikes and Wilf is accused of cheating. It's not true of course, but how can he prove it? Wilf remembers Weenie's crystal that was a disaster as it revealed events of the past rather than the future.