Based off StrifeCro's Grinder mage, I used to love his deck. Duplicate what you need and win by dumping Rag three times in a row ;)
For X matchup I duplicate :
Freeze mage : Loatheb / Healbot
Warrior : Anything big. Yes you will make warrior run out of removal, but it's a long game. Use your duplicates wisely.
Aggro : Sludge / Healbot. just stay alive hehe
The other matchups will depend
I chose :
Archmage instead of Boom : Boom screws up your duplicates while Archmage wins on it's own (simply op)
Nefarian instead of Ysera : Ysera is just too slow (sucks I know)... And having Ysera on board for too long will make you burn cards. Nefarian is just a more controlled version of Ysera
IMO the idea of the deck is to give you enough time/heal to setup your duplicates for big/useful minions. This is why there is so much heal in the deck. Of course, cleaning out a zoo's board is auto-win too.
There is no real bad matchup for this deck as long as you have enough time to do your stuff. Warrior and Zoo can be a pain