I upgraded Evil Snowman and it was working as it should until last week when I played my Ice wizard last, but today I've used it a couple times and it isn't giving me a shield against the target enemy anymore as it should be. I've checked and it is still upgraded, but not working the way it was. I also noticed the spell card says it's supposed to also give a trap to the enemy, but it has never done that since I've had it upgraded. I might have overlooked that part of it before, but it definitely did give me a shield but isn't anymore.
