I don't know... has so, so much CC already, i really wish you had made it a spell, which would fit the "mercy one, kill all others" theme on top of that.
Fire and Entropy also have a good amount of CC, ranging from single target to AoE. I don't see why Water shouldn't have an AoE spell, especially when numerous Water AoEs have been proposed on this forum. (It's also worth noting that Water is more reliant on Freezing than direct damage, which isn't as effective as pure damage in most cases.)
Themewise, I believe Light would be much more inclined to save everyone as opposed to one person given the "non-interventionist/helpful" nature of most of it's cards.
Though I dont want to comment on balance alone I think its overpowered with current values. I also dont think water needs such a powerful mass cc. I like the idea of it affecting both sides and not the creature you target as a unique mechanic but mass cc is not something that should spread from element to element. It makes them all feel too similar and ruins the whole theme of picking colors and the reason you do. I will sleep on this one and tell you how I feel later but I cant support it right now.
Compare Pandemonium, which unleashes a random effect on all creatures (some deal damage, which others are 1-for-1 card effects : Fire bolt, Ice bolt, Freeze, Gravity Pull, Shockwave, Sniper, Reverse Time, Drain Life, Infection, Lobotomize, Lightning, Parallel Universe ) and Rain of Fire, which deals 3 damage to all enemy creatures.
Unupped, Hailstorm does more constant damage but allows you to save a creature, which means you ideally will have to run only one creature or quint everything on your side, otherwise you will lose cards or have to spare your opponents.
Upped, Icicle Storm forces you to protect an enemy creature, which means that you may not be able to kill everything that you needed to kill with RoF, especially if multiple copies of one creature are on the enemy's side of the field.
As for Mass CC spreading, I doubt this is an issue as we current only possess 2 AoE spells in ETG, both of which are accessible by more flexible and 'complete' elements (
and
). Water is one of the weaker elements in the game and I believe it would benefit from having an AoE to kill enemies rather than rely on Freeze spam to a) Outstall the opponent or b) End the game before creatures unfreeze.