1000x!
Just beat Monster Monpiece's final boss (though there's some post-game content). Gameplay time is 26:25, (mind a decent chunk was probably spent sitting in the menus, let's say 20 real hours of gameplay to be safe). This is without touching the online multiplayer at all.
Prior to this point all of the packs in the game had 12 cards in them, 4 rares, which you'd get plenty of. Easy to get all the rares in four or five packs.
But after you beat it you unlock a super pack that not only has 100 cards (6 rares), but a number of them have -obscenely- low draw rates. To the point where it took me around 100 packs (of 3) to find one of the 'low probability' cards which wasn't even a rare. 0 rare pulls. Guess this is their idea of giving the game some longevity after you beat it..