I love "Ion Storm!" I will see where I can fit it in. I also like the use of Exava. However, "Cauldron of Souls" is rather pointless, as they all have persist or undying already. It wouldn't help my undying, that is a common misconception due to the rarity of the event occurring, but, when a creature has a +1/+1 counter on it and then has a -1/-1 counter place, it does not remove the original counter, it is just nullified.