When you play a tournament as Battlemage, and you have the Fire Aura ability (every creature that damages you loses 2 life), and you use the Skeleton creature (which deals you 1 damage when enters the game), so the skeleton loses 2 life when entering the game due to the Fire Aura :)
Same thing with Sea Sprite (when your water power is below your opponent's the Sea Sprite deals you 2 damage every turn, and also receives it due to fire Aura).
Not to forget when a Battlemage gets hit with Hypnosis and burns his own creatures! And for maximum comedy, watch a hypnotized vampire get burned by his master and then heal himself by drinking his master's blood! Add