I wouldn't sleep on this. This being Discoverable means you will hate playing against it. I wouldnt put it in my deck though unless I am playing some silly King P battlecry deck. Or in Wild playing Spiteful Summoner. I mean, if nothing else, in Wild, this is a buff to that card for Shaman.
Your completely right bro i although saw a new legendarie weapon for the shaman which cost 4 and has 1 4 statst his power is. If you play a spell summon a random legendarie with the same costst so i mean this 10 mana spell is worth it xD as contol shaman