Clairvoyance seems OP at first glance, but note it doesn't effect activated abilities. The only way to kill immortal creatures would be to draw and play clairvoyance (water) and then enough CC (ice bolt or not water) to kill them all, and all the cards must be in hand and playable that turn.
It isn't OP in my opinion, although water has some good CC, and can combo well with air.
I still dislike the effect BTW. I mean, when you play quint, you're supposed to have an immortal creature, and the card is balanced thinking in that. If someone made a card to deny it...
1) Quint/Anubis/Turquoise Nymph would need a buff (and the nymph already needs it). This can be discussed.
2) It'll be too dissappointing for the player. It's the same logic Zanz uses to reject discard as an effect. It will kill something you thought was safe, thus let down some gamers... Well, Zanz said something like this, I hope you get it
