I like finding ways to beat all the heroic bosses using one class, this week I was hoping for warrior but that wasn't working out so I decided mage would be best.
 
Instructor Razuvious:
 
Unfortunately I wasn't able to beat this one with mage so I opted for Icy's Priest deck (which I had to alter it a little because I didn't have some of the cards). It took a few tries but after getting the right hand I was able to defeat him, thoughtsteal was awesome if you happen to steal his weapon. Shall I become triumphant with a mage deck, I will update the post.
 
 
Gothik the Harvester:
 
Goal for this one, live until hes out of cards. Mage is good for this one because of the plentiful AOE's and Freezes. Also, you can destroy those pesky spectral minions with your own hero power.  The strategy is to take out his minions before you worry about him. When you get the spectral minions, either use sunfury protector to taunt them or use the silences on them.
 
2x Mirror Image 2x Voodoo Doctor 2x Frostbolt 2x Ironbeak Qwl 2x Sunfury Protector 2x Arcane Intellect 2x Frost Nova 1x Ice Barrier 1x Mirror Entity 1x Vaporize 2x Earthen Ring Farseer 2x Fireball 2x Polymorph 2x Spellbreaker 2x Blizzard 1x Argent Commander 2x Flamestrike   I might have switched Mirror Entity for another Ice Barrier but in this case it worked in my favor and gave me an Abomination which cleared the board for me after both Abominations died.     Baron Rivendare:   This one was pretty simple, I packed a few AOE's to take out the first 3 horsemen, (though I ended up killing them one by one because I wasn't dealt many AOE's at first). I also made sure to have plenty of single target freeze cards if his weapon got out of hand.    2x Arcane Missles 2x Ice Lance 2x Mirror Image 2x Mana Wyrm 2x Voodoo Doctor 2x Arcane Explosion 2x Frostbolt 2x Acidic Swamp Ooze 2x Kobold Geomancer 2x Arcane Intellect 2x Frost Nova 1x Ice Barrier 1x Vaporize 2x Earthen Ring Farseer 2x Fireball 1x Argent Commander 1x Flamestrike   He did a number on me before I got control and I was down to 5 health before I had killed the last horseman. Healing cards saved me.