Hearthpwn

Change it to: "After your hero attacks, Discover a spell with no targets, then cast it."

I remember it being mentioned on the stream when the card was revealed that Shaman have a lot of spells with no targets needed and those were the spells a player should look for when using The Runespear.  If that's the case, why not just limit the card pool to just those cards.

It could also be: "After your hero attacks, Discover a spell and add it to your hand.  It costs (0)."

A much more flexible option.  You could search for removal or lethal right away or save the cards for later when you need them.