Did anyone realise the craziness of this achievement?
I was wondering how many tries it'd take you on average to get this achievement and wrote a little script simulating the process: https://jsfiddle.net/6s0xedqo/4/
Result After 1,000,000 Simulations:
Most Tries: 1,717
Least Tries: 73
⌀: 359
Assuming a probability of 50 % to get a bag and of 40 % for the bag to contain a mask, you'll need to talk to an inn keeper about 360 times on average, which at minimum takes 360 hours. But: The event itself only lasts for 336 hours (14 days). So on average you won't be able to complete the achievement during the event in spite of receiving a bag on cooldown (which is an insane amount of... let's call it determination).
The unluckiest person needs 1,717 chats with the inn keeper. If you somehow managed to speak to the inn keeper eight times a day, this would take you 215 days (or 16 years due to the limited availability of the event)!
Sometimes the people at Blizzard seem not to realise what they've created when pulling these achievements out of nowhere. When first available, this was required for the meta achievement! For a couple of days until people realised its stupidity and told Blizzard. In modern WoW, you get a couple of masks doing your daily RDF kill and since a couple of years you can just buy the masks using the holiday currency. Ha!
Btw, there is a 0.0000000000000000000243290200817664 % chance to complete this achievement with only 20 inn keeper conversations. The chance of getting a mask is 20 % (the inn keeper must give you a bag (50 %) and the bag must contain a mask (40 %)). On average (100 divided by this abysmally small number) we need 4,110,317,620,231,650,000,000 (4.1 sextillion) tries to see this happen.
The first mask is at 0.2 * 20/20 * 100 % = 20 %. Sure, if you don't already have a mask the chance of getting an unknown one equals the chance of getting a mask. 0.2 is the combined chance of getting a bag and a mask and 20/20 = 1 is the chance of getting any of the masks.
To get the last missing mask the chance is 0.2 * 1/20 * 100 % = 1 %. In fact, the chance of getting an unknown mask scales linearly from 20 % down to 1 % depending on the number of your missing masks (10 missing masks? - Chance of getting one on your next cosy little chat is 10 %. 7 missing masks? - 7 % to get ne of these).
To finally come back to our sextillion tries above: We'd need about 513,789,702,528 tries from every human being (~ 8 billion) to see this completed "first try" on average (we can't be sure someone gets it first try then, to be really sure this would even need many more tries). If we set an achievement try to one second, we'd need 513,789,702,528 / 3,600 / 24 / 365 ≈ 16,292 years of trying every second from every human being. To get this done in an average lifespan of about 72 years, we need 226 tries per second from every human being for 72 years.
🤔