There is a new card out in the latest Hearthstone expansion, Whispers of the Old Gods, and it looks like this:
This is a good card. However, it is important to think about how and why it is good. A lot of people immediately jumped to comparing it to various cards that currently exist, and I want to explain why I think a particular comparison is most useful. First off, it isn't at all like Shredder.
Shredder is 2 mana less, and is deathrattle rather than battlecry. Useless comparison. A far better comparison is the Silver Hand Knight, which saw virtually no constructed play but which is a fine Arena card and honestly not that far off the curve.
The main thing making Silver Hand Knight unplayable is in fact Shredder itself. Shredder trades easily for Knight, and might even leave something behind if a 2/3 pops out of the Shredder. Normally a 1 mana cost increase gives +1/+1, so if the Summoner at the top summoned a 2/2 we could confidently say it would have the same fate as the Knight and be mostly forgotten.
But a random 3 cost minion is a *lot* better than a 2/2. In fact, you can expect an Attack value somewhere in the 2.6 range, and a Health value something like 3.15. That gives a total stat stick of 5.75, which makes the Summoner much higher value than the Knight almost by a full +1/+1. That is massive.
It doesn't end there though. Many of the random 3 cost minions have special abilities, most of which are good. You get a slightly higher than 50% chance of a good ability, and a small chance of a bad ability, and I roughly speaking think this works out to about a 50% upgrade chance, or at least that is my operating model. Some of those upgrades are somewhat weak, but some of them are amazing stuff like Divine Shield or Charge. Pretty much everything I counted was worth a stat point at minimum, and Divine Shield and Charge are much better than that, so I am confident you can count the extras as worth 1.25 stat points. That pushes the total stat points on the 3 drop of the Summoner to 7.
Given that you can expect a 5/5 and the equivalent of a 3/4 for 6 mana, is this a good card? Hell yes! Silver Hand Knight is only overcosted by .5 mana. It would be insane at 4, but is not played at 5, so it is a 4.5 mana card. Summoner gets 2.5 mana worth of extra stats on top of it, for the cost of 1.5 mana. Another way to look at it is that a 7/7 for 6 mana is a fine minion. (Ignore BGH for the moment.) Not superb, but would see play. Lowering the main body to 5/5 and getting a 3/4 is a massive upgrade, since you pay 4 stat points to gain 7. Even when you compare this to Cairne Bloodhoof you can't help but think that Summoner is strong. No matter how you look at it, 6 mana for the Summoner is a bargain.
Of course the Summoner isn't a neutral card, it is a Mage card. The question is, does Mage want an extremely powerful stack of stats for 6 mana? I think the answer is yes. Mage doesn't have a minion competing for that mana slot and would be happy to have something that can just be a big bunch of stuff. Because Mage has so much direct damage and because of their Hero Power, random stacks of stats are great because any enemy minions left over with low Health totals just die. Mage doesn't need specific sizes of minions, just lots of stuff, and Summoner delivers.
Nobody is arguing that in Arena this card is ludicrous, it is. However, I think that it will spawn a new type of Mage grinder / midrange deck that tries to get lots of value and just play a straight up fighting game in Constructed. Minions bashing into each other is the core of Hearthstone, and I think this card will cement that as a strong strategy.