Black Knight, Tinkmaster or Alexstrasza? I say Tinkmaster. He's useful in a lot of decks and functions as removal for big, powerful, minions where a 5/5 is easier to deal with.
In other words, I'm 99% sure I just played against a Bot in Casual mode. It was a Rogue and it went for the face regardless of everything. It was a very methodical process in which it played cards and attacked. The really odd thing was watching as each card would light up (meaning that the person is examining or clicking on it) and then my portrait would light up. Then at the end of the turn my portrait would light up about 6 times in a row. It seems that the bot would go through the player's hand, play any card that was possible and then attempt to attack the face with anything that was available.
The thing that made it pretty obvious was that he completely ignored the board state. There were times where it was obvious that I had lethal if he ignored things and he still attacked the face anyway despite being able to, easily, deal with the minions on the board. Then I, intentionally, let him pop my Ice Block and, again, he ignored my minions and kept trying to attack my face.
I'm normally a skeptic when it comes to these types of things and give people the benefit of the doubt (such as assuming a player is just new) but this was such an odd occurrence that I'm pretty convinced it was a cheat/bot program. It's also the second time I've seen this exact type of behavior (the first was about a week ago). Back then I thought the same thing but being the first time I saw it I brushed it off. But I'm almost positive it's a cheat/bot program.