Several new additions were added to Brawler’s Guild including twelve new boss fights. You’ll need to loot a specific item before you can purchase the challenge cards for each optional boss.

Item Boss Requirement
Knockoff Grumplefloot Rank 4
Grandpa Grumplefloot
Dance with Grandpa Grumplefloot in The Grummle Bazaar, Kun-Lai Summit.
Reward: Floot-Tooter’s Tunic
Hozen-Fur Fuse Rank 4
Master Boom Boom
Complete the The Burlap Grind daily in Kota Basecamp, Kun-Lai Summit and start killing Hozen until the item appears in your bag.
Reward: The Boomshirt
Raptorhide Boxing Gloves Rank 4
Ty’thar
Purchase some Raptorhide Boxing Gloves from the Darkspear Rebellion Quartermaster in the Barrens for the cost of one Radical Mojo.
Reward: Undisputed Champion’s Shirt.
Impeccably Sharp Tooth Rank 5
Razorgrin
Fish up an Impeccably Sharp Tooth from any pool in Pandaria.
Reward: Sharkskin Tunic
Vial of Reddish Ooze Rank 5
Splat
May be obtained from your Greater Cache of Treasures (random scenario reward) or Surplus Supplies (Barrens caravan escort).
Reward: Ooze-Soaked Shirt
Frost-Tipped Eggshell Rank 5
Dippy and Doopy
Battle Doopy (25 elite penguin) in the northern tip of Icecrown (47,14) to receive a Frost-Tipped Eggshell.
Reward: Tuxedo-Like Shirt.
Modified Chomping Apparatus Rank 6
Mecha-Bruce
Purchase the Challenge Card for Bruce (after you’ve defeated him in Rank 1).
Reward: Brucehide Jersey
Dusty Old Robot Rank 6
Blingtron 3000
There’s a chance to loot a Dusty Old Robot from your daily Blingtron 4000 gift package.
Reward: Last Season’s Shirt
The Bear and the Lady Fair Rank 7
The Bear and the Lady Fair
May be obtained from your Greater Cache of Treasures (random scenario reward) or Surplus Supplies (Barrens caravan escort).
Reward: Gorgeous Blouse.
Paper-Covered Rock Rank 7
Ro-Shambo
There’s a chance to receive a Paper-Covered Rock from harvested crops on the farm.
Reward: Paper Shirt.
Digmaster’s Earthblade Rank 9
Mingus Diggs
Complete Tol’vir digs in Uldum to receive Digmaster’s Earthblade. You can also hand in Restored Artifacts and convert Spirit of Harmonies for more Tol’vir boxes.
Reward: Digmaster’s Bodysleeve
Well-Worn Blindfold Rank 9
The Blind Hero
May be looted from the Darkmoon Game Prize after completing each daily at the Darkmoon Faire. Note: you will only be able to see the item if you are 90. Farming the item on lower level characters may still be done if you send the boxes to your Brawler character to open.
Reward: Sightless Mantle.

Once you have defeated all of the bosses above, you’ll receive the Wraps of the Blood-Soaked Brawler for Deck Your Collection.

I managed to loot the Dusty Old Robot from Blingtron a couple of days after the patch launched so I was eager to see what the quest was about. From there I wanted to work on collecting the others so I did some research and referenced them here. Quite a few were fun to collect as opposed to others which took some time and a lot of luck. The Hozen item took about 30mins while two came from the daily scenario bag as opposed to the caravan escorts. Sadly, the last item I needed was collected on an alt (two days in a row) while harvesting her crops but tonight I managed to collect the item from harvesting a normal crop.

Undisputed Champion shirt

So far I’ve defeated four and tried a couple of others but my question is now, how am I going to hold all these extra shirts?