@Promenius  
That still doesn’t make any sense. You already can’t see what you’re opponent is drawing.

@Ledvi  

 
I think the text means that your opponent will become unable to see how many cards you’ve got. As in, when you play a game you can’t see what kind of cards your opponent has, but you can still see how many they’ve got left in their hand.
 
It seems geared towards mostly a secrets-oriented deck… the way this could be used would be by dropping Queen Stealthalis on the board, and then popping one or more secrets in the same turn. Since your cards, secrets and mana would then be hidden from the opponent, they would be incapable of knowing whether or not you’ve actually used any secrets at all, as they would be unable to see secrets on the board, and they wouldn’t be able to see whether your hand became a few cards lighter after dropping Queen Stealthalis, and they wouldn’t be able to see your manapool drop either.
 
Still, it’s a pretty “meh” card overall.

But that doesn’t make any sense. You already can’t see your opponent’s hands.

very useless

I like the concept of this card, but I think it should be a legendary, and more importantly, those stats are wayy too good for how strong the effect is. Then again, most 6mana minions have incredibly powerful effects (Thaurissan, Sylvanas, …).
 
5/4 or 4/4 is probably a better statline.