Cheap Nefarian and Onyxia Priest Deck (Heroic Mode)

Strategy

The goal of this deck is fairly straightforward, to bypass the 2nd and 3rd phases of the Nefarian fight altogether by dealing more than 30 damage to him in a single turn. To achieve this, the goal is to get a Deathlord or a Lightwell onto the board early and then continue to buff it using cards like Dark Cultist, Temple Enforcer, Power Word: Shield, Velen's Chosen, Divine Spirit, and finally, Inner Fire.

Outside of these combo pieces, the deck plays various cards focused on dealing with Nefarian's Hero Power. Holy Smite and Holy Nova are both able to deal with the 4/2 minions very efficiently, while Mind Control Tech can help to recover the board if Nefarian starts to gain an advantage.

Although the fight can be won without Kel'Thuzad, getting this card into play behind a Deathlord is almost a guaranteed win due to a bug in the AI programming. If Kel'Thuzad is hidden behind a Taunt, the AI will stop attacking altogether, even if they have enough power on board to clear Kel'Thuzad afterward. If you are able to engineer this situation, you essentially have as long as you need to draw all the neccessary cards to buff Deathlord into a 30+ attack minion.

While this is happening, you will want to lower Nefarian to as close to 31 (30 Health + 1 Armour) as possible, without ever removing the last point of armor. Removing his armor entirely will initiate the Onyxia portion of the fight, which can be skipped entirely, along with the board clear that comes after it.