Way too slow and specific. This should have cost 4 mana at least. You can compare it with Mindgames
Versus agro both cards are useless
Versus midrange : you get 30% chance to get a good minion with Mindgames and you get instant board presence plus you get to play it next turn if it lives.
With Embrace Darkness you get 30% max to get the minion you've selected (if you're lucky), your opponent will likely silence it, kill it, evolve it or just kill you since you wasted 6 mana on previous turn, then if you still get the monster it will be on your next turn and this monster won't be able to attack until the next turn again.
Versus Control Mindgames gives even better results than Embrace Darkness
Mindgames is better than this card and nobody plays it. So I don't see any sense using Embrace Darkness