Hearthpwn

Coronius, as a lifelong (essentially) English speaker I would say that your English is fine. I was intrigued by your suggestion and think that it might have merit in any form of the game.

Imagine that a given deck begins to become oppressive. Those wishing to use it may continue to do so, but will have to face dealing with more than the expected share of mirror matches or contests against hard counters, as the oppressive class becomes banned by an ever larger fraction of the player base.

I could see this as a relatively simple alternative to nerfing. The question of "How hard to nerf and what are the unintended consequences?" is sidestepped. At the very least it would be an interesting experiment. 

Much hangs by the detail of exactly how the Shadow Visions treats duplicates, but let's give some principles.  Perversely, it is often easier to work out the chances of not getting the spell that you want, then your chance of getting the spell that you do want is 100% minus the chance of net getting it.  So if I have 8 spells and want just one of them, the chance of not getting it first draw is 7/8.  Assuming that the 7/8 chance came up, there are now 7 cards left, 6 of which I don't want, so the odds of not getting it with the second draw are 6/7.  If I was 'unlucky' twice, the chances are 5/6.  So my chance of not getting the card I want are (7/8)*(6/7)*(5/6) which comes to 210/336.  So my chance of not getting the card I want is 62.5% , making my chance of getting it 37.5%.  

Let me think. For 1000 gold I can get 10 packs come the next mini set. I very much doubt I'll be able to get that from Brawliseum. So, no thanks, I'll give it a miss. 

Curse my typing. Should be (27*26*25)/(30*29*28). My bad. 

Sorry, but your maths proves only that one can be really good at Hearthstone but not understand the math of probability. Your chances of not getting one of three key cards are 27/30, then 26/29 then 25/28. For all three to happen is(27*26*25)/(30*29*2) which is 17550/24630 which is 0.71 or 71%. So our chances of getting at least one of our key 3 is 29%. Of course if we swap those three cards we repeat the trial then our chance of 'failure' is again 71%, and the chance of two successive 71% events happening is (for cash) about 50%. So roughly half of the time we won't have a key card. Our odds are better on coin though.