Deck Your Collection (Season 1)

EDIT: As of this time, it is not known to what degree the second season of Brawlers' Guild will keep this information intact. It is possible new, Draenor-based sources for some of these cards will be added. I will keep an eye on this as it develops.

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"Deck Your Collection" - An Achievement in 12 Parts

First, you must acquire the Brawlers' Guild token through some action in the World of Warcraft. Then return to the Brawlers' Guild, turn in the item, and accept the followup quest. At this point you can purchase a card to fight the new opponent you just unlocked. Upon winning, you receive 50 valor points, a sack containing several hundred gold, and a shirt that grants on the wearer a buff similar to Precious' Ribbon.

The challenge card remains unlocked, so you can fight the battles again for fun if you so desire. Difficulty varies widely, but the majority of these fights will provide minimal challenge to a typical brawler.

Here is a list of the reported sources of each item:

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• Grandpa Grumplefloot - Knockoff Grumplefloot, found by going to the Grummle Bazaar in Kun-Lai and using the emote /dance on Grandpa Grumplefloot. May take a few seconds to work.
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• Master Boom Boom - Hozen-Fur Fuse, randomly gained from the Kota Kon daily in which you smash lots of hozen. Note that it is not tied to completing the quest, and appears to have a low drop rate so you may need to kill a great number of Hozen as the furious yeti.
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• Splat - Vial of Reddish Ooze, found randomly in caches from scenarios (e.g., Greater Cache of Treasure).
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• Dippy & Doopy - Frost-Tipped Eggshell, found by going to the northern tip of Icecrown and defeating an elite Penguin battle pet with your own team of battle pets.
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• The Bear and the Lady Fair (Argh and Raaaargh) - The Bear and the Lady Fair, found randomly in scenario-reward caches and the Heroic scenario daily cache, just like Splat's vial.
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• Mingus Diggs - Digmaster's Earthblade, found randomly while digging up artifacts for archaeology (Tol'vir confirmed). I personally just found one in a Tol'vir crate from Brann at the Seat of knowledge, after trading in various Pandarian artifacts for the crates.
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• Ty'thar - Raptorhide Boxing Gloves, purchased from the Darkspear Rebellion Quartermaster Ravika in Durotar, for the price of one Radical Mojo.
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• Razorgrin - Impeccably Sharp Tooth, found randomly while fishing in pools in Pandaria. The 'daily' fish migration pools appear to have a relatively high drop rate for this item.
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• Mecha-Bruce - Modified Chomping Apparatus, found by purchasing a challenge card to fight the original Bruce again and promptly obliterating the poor thing.
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• Blingtron 3000 - Dusty Old Robot, found randomly in Blingtron 4000 Gift Packages. Be sure to get your daily gift from him ON YOUR PRIMARY BRAWLING TOON.
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• Ro-Shambo - Paper-Covered Rock, found randomly while digging up vegetables on your farm. Special crops do not work.
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• The Blind Hero - Well-Worn Blindfold, found in the prize caches from doing Darkmoon Faire dailies. These bags are not bound to the character who earned them, so you can mail them to your main for opening. Indeed, you could roll numerous level 1 characters to play the games if you had terrible luck with the blindfold.
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Note: Despite being one of the easier-to-acquire, the archaeology token leads to one of the hardest Brawl fights currently in-game. If you are still gearing up, consider pursuing that token last to avoid the frustration of having the token before you have a chance of beating Mingus.

I can confirm that if you kill each boss as you unlock it, you will retain credit once you go between Collect Your Deck and Deck Your Collection.
In my case, Paper-Covered Rock was my last item and I had killed every other boss first. Upon turning in the Rock, Deck Your Collection had credit on every boss but Ro-Shambo. So, 1 more kill and achievement earned.

tl;dr you don't need to save all your quests or kill the bosses twice, you still get credit even before this achievement is visible to you.

Edit: Will also add, that the coin bags you get as a reward from each quest will give you 100x brawl level gold, meaning 600g from a level 6 brawl etc. This gold counts towards Got My Mind On My Money

All of the gold bags add up to looting 6900 gold from these 12 bosses. That looting counts towards achievements that track looted gold.