Spirit Lash seems decent if you can pair it with spell damage. In the case of a full-ish enemy board, Spirit Lash + Thalnos would be "cast Consecration, draw a Card, heal 10-16 HP". The other thing to note is that it fits into Wild Pyro/Northshire/Circle strats for massive card draw.

I'm not convinced it beats out Priest of the Feast/Binding Heal for healing back up, but the card is borderline enough that I'm not prepared to call it crap yet. I am generally more excited for Priest getting some decent Deathrattles though. The main thing Deathrattle Priest lacked was a win condition, as just playing a load of sub-par Deathrattles a couple times over wasn't all that great. With Deathrattle being a major theme of the expansion I'm betting there will be some power cards to make building a deck for any class viable. Priest having a Reno effect available might just give them the edge.

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I'm very curious to see how the Hunter power works. Card text is limited in space, so what happens when you get a card with two very complicated texts? For instance, Bittertide Hydra combined with Giant Sand Wurm. I suppose they could get around it by adding the card text of the second card as an enchantment - but then, how do they show that for a card in your hand with two Battlecries?

Also, if you go over 10 mana with the combined card, will it just be an unplayable card? That seems like a major downside if you get a pair of really expensive minions. Let's say you get offered Ultrasaur, Giant Mastodon, and King Krush on your second pick. Unless you picked a 1-mana minion, you're now screwed because the Beast you created will be guaranteed to cost over 10 mana - literally unplayable.

It also seems a bit slow. While the stitched together minions can be powerful, they also cost 2 mana more than normal. A lot of cards become non-viable if you increase the cost by 1 mana, and you're combining the mana costs as well. This makes the minimum cost 4 mana for double 1-drops, and the cost escalates really fast as you combine even relatively small minions. For example, spending 2 mana to draw a Carrion Grub and Infested Wolf is pretty good. The mash-up is a 9 mana 5/8 that Deathrattles into two 1/1 minions. You're going to be pretty sad when that gets Hexed.