Hearthpwn

This is the deck used to beat both Anub'Rekhan & Grand Widow Faerlina in normal/heroic modes.

Make sure to upvote if you found this deck helpful and you've used it to successfully defeat them!

A member made a video of the Anub'Rekahn fight using this deck for those who which to see the video here, it will be at the bottom of the page.

Naxx Reminder

Sometimes you will get bad hands/draws as the match progresses, making it harder to come back or keep said taunts up and kill them. If this happens try again, until you get a good hand and good follow up draws. You will beat them, just keep trying! :)

Mulligan

You want to Mulligan aggressively for Wild Growths and Keeper of the Groves against both of them.  You need to ramp up to your taunts as fast as possible.

Strategy

1. After the Mulligan phase is gonna be one hard match no matter what. Wait till turn 2 to Wild Growth to set up for bigger minions. You want to keep Keeper of the Grove as a battle cry kill X card only for Anub'Rekhan, for Grand Widow Faerlina you can keep it as 2 damage or for the silence depending on the situation. 
2. Only play taunt minions as you ramp up for "MAX VALUE". Cards like Chillwind Yeti, Earthen Ring Farseer, and even Harvest Golem don't give you the value if you don't follow up with a Mark of the Wild and/or Defender of Argus immediately after playing them.
3. The key is to keep stonewalling your opponent into making 2 for 1 or 3 for 1 trades, shielding your health as much as possible. Never control the board, always go for the face. 
4. There will be times were controlling the board is to your advantage, but in most cases it won't be. Be on the lookout for those moments.
5. Against Grand Widow Faerlina you want to control her Worshipper minions in heroic because they give her +3 attack each and she will place anywhere from 1-3 of them in back to back turns. If unlucky she might even place 2 on the same turn. You want to kill these because she will use the attack gained by them to more quickly and easily go through you taunts, thus lowering you taunts potential and killing you that much faster.
6. Keep bashing them both in the face, and putting taunt after taunt up to maintain your health. They voluntarily trade into your minions so you don't have to control the board xD
7. Wrath can be use to either clear 1 minion off the board or to draw a card if you can kill a minion of with the 1 damage , but always try to get maximum value from it.
8. Swipe has to be use to clear minions ASAP, or if your taunt walls are healthy and your in a far ahead position to do 4 damage to them, as this is who kills who faster. In heroic mode you will be using this to clear minions as they get on the board, using it as 1 of your 2 "minion control" cards, while your taunts bash them in the face. Don't be stingy with them either. Using it to clear 1 minion with high damage and health will only serve to "extend" the life of your taunts which is exactly what you want. The longer your taunts stay up the more damage they can dish out, and soak up.

Alternative Deck

For an alternative version of this, that is a bit more expensive in dust, but works just as well, if not better check out My Budget Ramp Druid. It will be a more fleshed out version that also was able to beat them both.