I did it, Reddit. I killed the Cow King *AS* the Cow King.

It took a looooong time to get the setup to work.

http://imgur.com/a/vpdkz

http://imgur.com/a/4TCek

http://imgur.com/a/qDDzs

Here's how you do it: You'll need a priest deck with Mass Dispel, Sylvannas, Drakonid Op, Dragonfire Potion, Thaurissan, Youthful Brewmaster, Lorewalker Cho, and Mind Vision. Plus whatever you feel like adding to survive and trigger the secrets (dragon priest works well).

You need to make sure the last secret triggers on your turn. If it triggers on the AI's turn, then he'll just turn into The Cow King when your turn starts. By far the most annoying secret is the one that requires you to take lethal damage, since doing that on your turn as a priest requires a weapon or Blackwing Corrupter, and being at a very specific health total.

When the portal comes down, drop Mass Dispel to silence it. Technically this step is optional, but it makes life a lot easier. No stats are displayed, but the portal is actually a 4 mana 0/10, so make sure you don't play Shadow Word: Horror or too much AoE once it's on the board.

If you drop Drakonid Op, look for Shadowflame. Otherwise, try to get a Thaurissan tick to hit both Sylvannas and Dragonfire Potion (or one of them twice). When you're ready, drop Sylvannas with the board clear to steal the portal. Then put it in your hand with Youthful Brewmaster.

Finally, empty your hand of everything except Lorewalker Cho and your two Mind Visions, drop Cho, and play one Mind Vision. When the AI plays it, they'll either get the portal, or another Mind Vision (make sure to dump whatever you got off the Mind Vision, if anything).

Once the AI drops their portal, you're free to drop yours. Congratulations, it's time for a Bovine Brawl.