This card is definitely too easy to play for what it does. Combine it with Merchant or any card that can give you gems at round 1 and your opponent will feel himself very uncomfortable. Play it twice and... well, playing with Dungeon 1 is pain and suffering. Old nerf didn't solve this problem - it's still widely used and very, very effective.
I suggest to change its cost to somewhat similar to
Kidnap. Say, 8B/16G.
By the way, you can also rebalance Kidnap to 8G/16R...
[moderator DPsycho: added card link to Kidnap for ease of navigation]