Greater Darkmoon Card

creates a random card out of: Ace through Eight of Furies/Lunacy/Blessings/Storms.
item links: (cards, deck, endreward)

1-8 Ace of Furies . . . . --> Furies Deck . . . --> Darkmoon Card: Vengeance
1-8 Ace of Lunacy -. . .. .-> Lunacy Deck -.....-> Darkmoon Card: Madness
1-8 Ace of Blessings .. .--> Blessings Deck . . --> Darkmoon Card: Crusade
1-8 Ace of Storms . . . .--> Storms Deck . . . .--> Darkmoon Card: Wrath

Given the fact that this will create a card of not just a random deck, but also a random number, I can't imagine too many people will actually bother using this for anything more than levelling up their inscription skill.
You'd need to make an absurd number in order to come up with a full deck, so realistically they need to be auctioned in the hope that someone will need the card to help complete a set they are after.

The problem with these decks is that you'll end up with a whole lot of duplicates. The more decks you make, the smaller this effect, but it still pays to know just how many cards you can expect to make.

To this end, I programmed a sim that randomly draws cards and checks how many duplicates you end up with for a given number of decks. This is obviously only valid for creating decks within one set (i.e.: classic, TBC, WotLK, Cata). Here are the results (up to 109, as this is the maximum amount of decks anyone would need to reach full exalted with Darkmoon Faire).

Cards needed per deck to create a given number of epic decks

decks cards per decks cards per decks cards per
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1 52,51 41 12,11 81 10,81
2 35,18 42 12,05 82 10,79
3 28,64 43 11,98 83 10,78
4 24,99 44 11,95 84 10,75
5 22,77 45 11,91 85 10,74
6 21,10 46 11,85 86 10,72
7 19,81 47 11,81 87 10,71
8 18,88 48 11,76 88 10,68
9 18,10 49 11,72 89 10,68
10 17,49 50 11,66 90 10,65
11 16,93 51 11,62 91 10,64
12 16,49 52 11,60 92 10,61
13 16,08 53 11,55 93 10,61
14 15,70 54 11,51 94 10,58
15 15,43 55 11,49 95 10,58
16 15,16 56 11,45 96 10,55
17 14,88 57 11,41 97 10,55
18 14,63 58 11,39 98 10,52
19 14,43 59 11,35 99 10,51
20 14,23 60 11,31 100 10,50
21 14,04 61 11,28 101 10,50
22 13,89 62 11,27 102 10,47
23 13,73 63 11,23 103 10,46
24 13,61 64 11,20 104 10,46
25 13,47 65 11,18 105 10,43
26 13,33 66 11,15 106 10,43
27 13,24 67 11,13 107 10,42
28 13,12 68 11,10 108 10,40
29 13,00 69 11,07 109 10,39
30 12,92 70 11,04
31 12,84 71 11,02
32 12,74 72 11,00
33 12,65 73 10,97
34 12,58 74 10,95
35 12,50 75 10,93
36 12,42 76 10,91
37 12,34 77 10,88
38 12,29 78 10,87
39 12,21 79 10,85
40 12,16 80 10,84