Hearthpwn

After my first couple attempts, I was afraid that this boss would require a huge list of legendaries to beat.

You really don't need all that.  I just beat him today using almost all common neutral cards, plus Kel'Thuzad.  I don't even have a Sylvanas or any Force-Tank MAXXs of my own.  I feel like the list presented here doesn't have enough threats that can handle Drakkisath's high toughness minions.  Guys with 4 power just don't cut it (Sunwalker excluded).

I played with War Golem, Stormwind Champion, Core Hound, Lord of the Arena, Boulderfist Ogre.  Basically any high power/toughness minions you have, plus Kel'Thuzad.  Faceless Manipulator is great to copy your Kel.  I fleshed my deck out with a Ragnaros, Stalagg, Rend Blackhand -- really not an ideal team, just all my high power minions.

Hero choice isn't super relevant, but I played Priest and included Mind Control, Shadow Word: Death, and Resurrect.  I got lucky with Resurrect bringing Kel'Thuzad back.

It took me 5 or so attempts, but way fewer than I had feared.  The trick / luck is to stick Kel and then leverage him hard.  Just hope Drakkisath doesn't play Twisting Nether.

Incidentally, I was running Sunwalkers, and it seems like Drakkisath chose not to attack sometimes when it might have been advantageous for him to have done so.  Not sure if this is an AI glitch, but he was way more passive than he needed to be when I had Sunwalker + Kel.

This is the most expensive deck ever.

Yup lol, just pick your best cards. There's a ton that can be switched out. The only mandatory cards are board clear (eg. twisting nether and doomsayer +  bgh). I picked cards like void caller just because they're sticky. This isn't a joke deck, the matchup really is better with quality cards.