Fair, Uncommon, 5b 5r
Discard all non-common cards from your hand.
For each uncommon - Stock +3
For each rare - Stock +6
This card would throw Nature far off balance. Nature presently makes summoning Rares very easy, but those Rares are expensive. With this card, you could cash them in for a realistic 15-20 stock. The cost of playing this card isn't even prohibitive as you don't have to spend any gems to pull it off. As soon as you draw another Uncommon Nature, possibly immediately as you're refreshing much of your hand when playing this effectively, you can have another Rare Nature in two tuns and be able to play it and draw another almost right away.
This is arguably effective with Illusion as well, though Illusion isn't kept in balance by featuring expensive cards, so I don't think it's as big a deal on that front.
TLDR version: This card would be a huge and unintended Nature buff.