@Marioland  
The only upside is it also hits the enemy hero, but then why not just run Hellfire? A lot of Warlock cards are designed around “High Risk, High Reward” Low mana costs for the damage, but it tends to have a downside to compensate. I’d still run Shadowflame or Hellfire or Twisting Nether for a board clear.

@Ledvi  

 
In that case, it’s far too weak. You might discard 4 cards to deal a Flamestrike to the enemy board and face (a total cost of 5 mana and 5 cards in total), but then you’ve got no hand to contest the board and low amounts of mana to take board control back. It’d have to be a Turn 7 play at the earliest so you can life tap afterwards, but that leaves you with nothing on the board and gives your opponent plenty of time to seize the day. Basically, if you don’t win the game specifically by playing this and killing your opponent with it, you’re screwed. You don’t get riskier than that.
 
I’d rather run Shadowflame and use only 4 mana and two cards (counting the minion, which may or may not have already gotten value by that point) to clear the board instead of discarding a whole lot of cards and spending and leaving myself dry without a hope of coming back.

@Marioland  
You deal damage per card, not per mana point.

So, put a bunch of giants in your deck and win on Turn 5 with a single card.
 
Yeah, nope.

Seems like an unreliable Consecrate or Holy Nova. And Warlock already has a nuke spell.

Interesting. :) I’m not really sure what to do with it, though. It leaves allied minions standing, unlike Deathwing. But could you really rely on your ability to save enough allied minions especially if you’re letting the enemy build up an opposition? I can’t think of a 5-mana creature (at 10 mana) to drop that’d be enough of a counter-force after I lose all my cards.  
It has an advantage of affecting multiple creatures over the “Forbidden..” cards, but I don’t think the extreme cost is worth it.
 
I think it underestimates the power of extra cards, honestly. In Hearthstone card advantage is EVERYTHING. Enough that a Warlock would spend the whole game harming himself just to build one. Cards that drop Deathwing or use “Discard…” cards heavily tend to be ones that play towards 0 cards in hand in the first place. Without enough cards in hand though, this one is worthless. With cards, it just sacrifices a huge advantage.
 
Maybe if it was 0 mana, I would consider it. As it is, why would I waste my cards when Mage board clearers let me keep them and have the same relative mana cost?

The card really should specify the amount of what.  
Presumably cards, but currently it does not say that, and doesn’t even imply it particularly strongly (It’s just the only number you’ve got, so it’s the most likely one you need to use)  
Heck, I feel it shouldn’t even say ‘amount’ but ‘number’ of cards - number implies you want them counted in individual cards, ‘amount’ could be anything from volume to weight to the desired individual cards.

@Divad  
Since handlock is one of the most popular and annoying deck that warlock players uses, I decided to make a spell card aiming towards that. Also, you are almost correct. If you wish to destroy a single card for max hand, then you will deal ten damage total.

So at max it can do nine damage if im reading it right. But if you do it when you get five mana youd get 5-6 damage. But most minions would die, so not a bad card