Very straightforward, some if not all battlecast abilities are active on defense after the latest update. Notice how serpent has the thor relic's vigor buff on defense. Most of the abilities don't matter much on defense, but then you have serpent who's getting an extra ~15% attack boost for free. I thought the plan was to only implement stat casts on defense, so this just looks like a mistake will probably cause some balancing issues (again, +15% damage serpent).