One of the cards I love the most in Hearthstone is Fel Reaver. I haven't used it a lot but I love it because it changes the game in a big way when it lands, by offering the opponent a new way to win the game. It isn't often that you play a card that says "Hey opponent! Want a new win condition? Here ya go, try and deck me!" and that makes it a card that generates a lot of interesting decisions.
The thing about Fel Reaver that makes it so powerful is that people who play against it in a draft situation lose their minds. It is +2/+2 bigger than a minion of its cost has any right to be and that is hugely powerful, but people make all kinds of mistakes when it gets played that makes it even better than that. Usually this involves them trying to deck the owner of Fel Reaver by playing tons of cheap cards and leaving Fel Reaver alive, hoping to make the decking option work.
Look at the numbers: Most of the time a Hearthstone draft deck goes through 15 cards at most in a game. Often less, rarely more. Given that decks are 30 cards this means that the first 5 cards you play against a Fel Reaver do literally nothing. Oh, they look impressive, burning away the opponent's options, but they don't offer any useful advantage. At the end of the game if you are dead it does not matter at all if the opponent happens to have no deck left, and it takes a couple of turns after their deck is gone before they really run out of options and lose.
The trick to fighting against Fel Reaver is to pretend it has no text. It is just an 8/8 for 5, nothing more. Sure, if you happen to pop off a few cheap cards before blowing it up there is a 1% chance it will help you win an attrition match but you are better off ignoring that. The most important thing is just focusing on winning the game right as it is.
The same sort of thinking has to apply to the other side too. When you have a Fel Reaver don't worry about your deck - just try to win the game. Remember that if the opponent tries to ignore Fel Reaver and deck you then you can always just run Fel Reaver into their minions and get good trades, and if they throw their minions and removal at it then all well and good, it did its job of being a gigantic body.
More than anything everyone involved has to remember that although you *can* deck someone using Fel Reaver it isn't a quick process, and Fel Reaver probably kills you in three swings. Unless something weird happens you need to focus on winning the game normally, not on the new win condition that just appeared to taunt you from a great distance.
It reminds me of a team Magic tournament I participated in years ago where my team was playing W/U Millstone. We slowly ground away our opponent's decks and won convincingly, and at the end of the game the opponents tried to get us to trade them some Millstones.
We tried to explain to them that they didn't lose because Millstone is powerful - they lost because our decks dominated them and they sat there doing nothing. We could have won with any card, and in fact I used Serpent Generator to much the same effect in later times.
However, they remained fixated on the awful feeling of their deck being ground away. There is something very powerful about watching your resources drain off, even when that resource drain has little to do with actual victory. Seeing cards flip from the deck into the graveyard is an emotional event from both sides, far more so than its effect actually justifies.
Fel Reaver and Millstone are the same in this way. The takeaway lesson is to focus not on the cards flipping off the deck, but on what actually makes you win or lose. In both cases the thing to do is ignore the milling effect and focus on winning the game right now, because that is what matters in nearly every case.