Wow, that's a new kind of slow.
9 mana, deathrattle instead of battlecry, no taunt (obviously), or lifesteal, or way to encourage the enemy to kill it, healthy enough to survive all damage-based AoEs, 3-attack, that basically threatens nothing late game. I guess it can be combo'd with Naturalize to get all the value in the same turn, but still you waste your own removal and give the enemy two cards...
How much does Blizzard expect the meta to slow down? Seems like they are getting carried away with the slow legendaries right now. These cards are always a waste unless you give ways to suppress aggro.
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2
For the most part, this is an arena card. It could potentially net better spells than you have drafted or simply be a 4/5 body for 4 mana which is good enough. Other legendaries will be more likely picked though.
3
If it was only your cards, this would be very good. But it encases all minions that died this game. So pretty much an average arena card.
1
3 mana 3/3 that casts Ancestral Spirit. Except it can be used in any class. Definitely a playable card, but doubt it will be used in constructed. Arena however will likely love this card.
5
This card is not as simple to evaluate as people might think. While it is 8 mana and seems bad, keep in mind one reason why Mysterious Challenger saw a lot of play. It cycles cards out of your deck. I could see this being put into freeze mage for that purpose, but they tend to only run 2 kinds of secrets. So if it did see play, it would likely be a one of in the deck.
Edit: If we do base it on only pulling two secrets out of your deck though, here is the value you are really looking at:
Arcane Intellect (3 mana) + playing the two secrets (3x2)= 9 mana in an 8 mana card. So you need two secrets to become active to obtain value in this card.
2
The key difference though is that Thrall, Deathseer has an immediate effect when used. So played correctly, you could end up with a massive tempo swing. You are not wrong about the hero power though. Even though the hero power can be used in unique ways that would benefit you like transforming a minion that traded and has one health into something else. It does have that drawback in that it could turn into something worse. I would still put this as slightly above average overall though.
2
This card could be good depending on a single factor that I doubt will actually happen. When the card is controlled, are you able to act with it immediately? Most likely answer is no which means it is dust. If by slim chance it does allow you to act though, then this could be worth experimenting with even though it is still slow.
1
Dear god. I admit the effect is insane in what it does. But holy hell is it bad to do that. If it said something like "Switch your deck with your opponent's" I would much rather go for that.... although that would be pretty OP XD.
14
If you have 2 in your deck and both are used. The probability of removing a key card like Archmage Antonidas in Freeze Mage of the 30 available is 6.67%.
5
While this card sucks.... that art is amazing!
2