1) They're desperately trying to make Discolock a thing
2) There are no words to say how bad this is.
You need to play it to an empty board, and even so it's very easy for the right kind of deck to tag it a handful of times and empty your hand. It's a case in which the /6 body is actually a drawback because you can lose multiple cards. There aren't enough demon buffs to make your opponent pay for leaving this alive, and not enough cards which give a benefit on discard. It's just bad.
This is a combo card people. Don't look at it as a tempo play (which it could be if you're holding golems). You can rapidly complete your quest, which means you hardly need a strong hand at the time, or completely destroy your opponents hand with treachery in the late game.
If they want to make discard mechanics work together they need to give the player some control over what is discarded. As many others have suggested discarding the lowest cost minion/card instead of just random. Hell I even think if you chose which cards to discard the deck would maybe just be tier 2 at best.
Also please please stop giving Warlock terrible cards, I know you are scared of lifetap but if that's the case then just redesign the hero power and let Warlock get something half decent. This class has been given so much awful shit starting after GvG.
Priest design philosophy: If they can't have good cards, let's let them steal the good one from their opponent.
New Warlock design philosophy: If they can't have good cards, let's equalize the playing field by allowing them to discard the opponent's good cards. Of course I am referring to donating this with Treachery followed by a well placed Defile.
A problem with using this in Lakkari Sacrifice is your opponent can actually discard your Nether Portal if they hit it again after you complete it. So, yeah, seems like Treachery shenanigans is the most consistent way to use this thing, but that seems weak too.