Maexxna's hero power might be countered by using minions that have battlecries that do damage. Examples: Stampeding Kodo, Abusive Sergeant, Elven Archer, Stormpike Commando etc.
My plan is to focus on minions with charge, and something else that I noticed yesterday. If you look at my screenshot above, you'll see that I have a
ton of those oozes. How did I do that? I only started with two ooze cards, but they create clones and Maexxna kept sending one back! So, that gave me an idea... why not use minions that summon other minions? If Maexxna is going to send two back, and she sends a minion with a summon back, then I get more creatures on the board!
I think those combined with some good charge minions would be quite potent. Also, Maexxna's hero power sends two minions back
and it's free. I was watching TotalBiscuit try it with his gimmick decks last night, and the thing is... she did it every time. That means you can use charge minions and not potentially lose them. So, all I can say is...
Leeeeeeeeeeroy Jeeeenkins!
EDIT:
Although, my only worry for using summon minions is that I could end up with a rather full hand if she starts ending back the summoned minion. For example, during the Rogue class challenge, I used the 2/3 that summons the 1/1 ("Don't mess with tusker!"), and the 1/1 ended up costing me 1 mana to put back down.