Hearthpwn

Would be a cool card if it was 2 mana.  Don't think this is good enough for 3 mana since HK is too situational and on it's own dealing 3 damage for 3 simply isn't good.  Could see it maybe getting buffed to 2 mana in the future to keep it more in line with a card like Frostbite. 

I completely agree the 3 mana cost makes it just bad even when you build a deck just for fun.
And it would even be justified to make it target only minions. Rogue doesn't need more face damage spells, if there's gonna be a viable meta deck like garrote rogue they have no problems playing sinister strike or opening with the si:7 spell, so they don't really need more face damage, especially not for 3 mana. But Rogue does need more cheap board control with good value such as the resource generation here.

A 2-cost 3 damage to a minion spell would be the main reason to play it while the resource generation would be an added bonus - nothing too OP for rogue, it doesn't generate tempo.

For instance it would be much more useful with preparation and allow rogue to more easily generate random shenanigans without risking too much. And these decks (Galakrond rogue comes to mind too) are never OP combo or aggro decks, so they rarely dominate the meta, if ever. So there really is nothing to worry about :D

Though the downside would be no honorable killing the enemy hero and getting the discover options blurred just before appearing.

God its so bad.

Great, another face race spell.

yay more face damage spells for rogue

3 damage HKs are easy to line up, it can go face, I wish these "discover a card from another class" effects were more specific somehow, but I think this is good.