Collect Your Deck (Season 2)

This achievement is rewarded for collecting each of the following items and handing them in at Brawl'gar Arena. Each item rewards you with the ability to purchase the Challenge Cards for each listed boss. Once a boss is unlocked, you can purchase the card in order to challenge them, and receive a quest to defeat them in (allegedly) single combat.

Defeating each boss unlocked in this manner, and handing in the quest to do so, earns you a chunk of gold (and amusing vendor trash items worth more gold) from [item=98099]. In addition, each boss rewards a rare shirt for defeating them, such as [item=98081]. Finally, defeating ALL the bosses earns you the sequel achievement, Deck Your Collection (Season 2), and the epic shirt [item=98543]. If you lose these shirts, you can re-purchase them from [npc=68363] for Alliance, or [npc=68364] for Horde.

The items, their sources, the bosses they summon, and a brief rundown (as available) follow.

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• [item=97978] - Given for targeting [npc=71082] at the Grummle Bazaar in Kun-Lai and emoting /dance. Unlocks Grandpa Grumplefloot ([quest=32837]).
  Grumplefloot summons luckydos, which you simply need to avoid. No particular trick here.
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• [item=97979] - Randomly contained in [item=92813], the Random Scenario rewards. Also potentially looted from [item=97954], rewarded for escorting Darkspear and Bloodhoof supply caravans in the Northern Barrens, or for overturning Kor'kron ones. In Draenor, this can be looted off of Sargerei enemies in Shadowmoon Valley or Talador. Unlocks The Bear and the Lady Fair ([quest=32839]). A reference to this song from A Game of Thrones.
  Several trampolines will spawn around the arena. The idea is to bounce across them in sequence; chaining three bounces together will briefly buff your damage, and also allow you to reach Argh's platform to DPS her. While ranged can technically DPS her from the ground, Raargh will likely eat your face before you can defeat them.
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• [item=97980] - Randomly awarded from killing hozen on the Burlap Trail while on the daily quest The Burlap Grind. Unlocks Master Boom Boom ([quest=32841]).
  Throws dynamite at you, which you just have to step away from. Periodically, he will spawn a Boom Box, with four fuses leading to the edges of the arena. You must stomp on (walk over) the sparks on each fuse before they reach the center in order to avoid being oneshot.
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• [item=97981] - Caught from Pandaria fishing pools, or randomly contained in [item=112623], from Draenor Garrison Fishing Shack daily quests. Unlocks Razorgrin ([quest=32843]).
  Razorgrin flops around the arena and oneshots you if he touches you, not very much differently from Dippy (except without the free knockback).
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• [item=97982] - Randomly contained in [item=92813], the Random Scenario reward. In Draenor, dropped by [npc=78259]s in Gorgrond. Unlocks Splat ([quest=32845]), the Simon to [npc=67595]'s Hans Gruber.
  Similar to Blat. Splat's clones hit much harder, and she has a great deal more health. In addition, she leaves toxic pools behind as she oozes along the ground, necessitating that you make good use of the limited room in the arena.
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• [item=97983] - Dropped by Bruce, the first boss of the Brawler's Guild. If you defeated him prior to the launch of patch 5.3, you can summon him through the use of [item=93823]. Unlocks Mecha-Bruce ([quest=32847]), making his triumphant return from the chomping jaws of defeat.
  Mecha-Bruce has significantly more HP, and can stun you for 3 seconds, necessitating that you run away during his "Harder, Better, Stronger" ability in order for the stun to wear off before he reaches you for his next Chomp Chomp Chomp Chomp.
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• [item=97984] - Dropped by defeating Doopy, an elite battle pet in northern Icecrown (on the glacier at the very northern tip of the zone, where all the [npc=32498]s are). Unlocks the southern seabird siblings Dippy and Doopy ([quest=32849]).
  Doopy acts exactly the same as Dippy, but moves much more slowly. Switch between them to keep them both off you, but make a priority of burning down Dippy first since he gets back in range faster.
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• [item=97985] - Has a chance to be contained in [item=86623] or [item=113258] -- note that you can only get one of these per account per day. Unlocks its own stunning self, Blingtron 3000 ([quest=32851])!
  Blingtron 2000s will continuously spawn from a pile of gold near the boss (who is immobile) You must kill them at short distance intervals between the boss and the Gnomish Tesla Coil in the opposite corner, then activate the Tesla Coil to create a massive burst of chain lightning that short-circuits the boss.
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• [item=97986] - Lootable when collecting Tol'vir archaeology fragments from either dig sites or a [item=87539]. Unlocks Mingus Diggs ([quest=32853]).
  Mingus is immune to damage until you slay the four statues he brings into the arena with him. Each statue will rapidly stack a short-duration DoT on you if you are not in melee range of it; you must rotate through them in order to allow the debuffs to fall off in turn. One strategy is to use your DPS cooldowns at the beginning to burn one statue to 0 immediately, since survival becomes easier as you slay each statue.
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• [item=97987] - Lootable from [item=93724]. Unlocks The Blind Hero ([quest=32855]), a figure shrouded in darkness. Literally.
  The Blind Hero performs large cone attacks with his sword, and periodically charges you if you move out of his melee range. Simply avoid the cone attacks and DPS him.
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• [item=97988] - Lootable from vegetables harvested from the farm in Valley of the Four Winds. Unlocks Ro-Shambo ([quest=32857]).
  Ro-Shambo plays Rock-Paper-Scissors with you periodically (as indicated by his name). Depending on whether you win, lose, or tie, an add of varying strength will be summoned; if you win, Ro-Shambo will additionally be stunned and take 500% extra damage for a few seconds. Although Ro-Shambo's first throw is random, he will always cycle through his choices after that in Rock-Paper-Scissors-Rock order, and Scissors is the most difficult loss to survive. Thus a generally optimal strategy is to choose Scissors the first time, then choose appropriately the second time based on what he throws if you haven't killed him.
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• [item=97990] - Purchasable from the Darkspear Rebellion quartermaster, [npc=71226], for one [item=97849] (rewarded from the weekly quest [quest=32862]). Since the Darkspear Revolution is over now, this item randomly drops from killing level 90 mobs in Northern Barrens. Unlocks the troll boxer Ty'thar ([quest=32859]).
  Ty'thar is a reference to Mike Tyson's Punch-Out! and has similar combat structure. You must dodge his jabs and slam by moving left, right, and back. Three knockdowns constitutes a loss for either you or Ty'thar.

Thanks to the Wowhead community for their invaluable ability to glean every last bit of information on this sort of stuff from the PTR.

Given for finding each of the hidden items that unlocks a unique fight in the Brawler's Guild. Here is where each of these items can be found:

[item=97978] ([quest=32837]): Perform a /dance with [npc=71082] in Kun-Lai Summit.

[item=97980] ([quest=32841]): Accept the daily quest The Burlap Grind in Kun-Lai Summit and run around slaughtering Hozen while riding Kota Kon until you receive this. You do not need to actually complete the quest and you can still receive it even if you have already completed the requirements for the quest.

[item=97982] ([quest=32845]): Chance to find this inside of [item=92813] earned from running Random Scenarios.

[item=97984] ([quest=32849]): Earned by defeating the Legendary Battle Pet Doopy. He can be found in Icecrown located on an ice shelf north of The Shadow Vault at location [48, 14].

[item=97988] ([quest=32857]): Chance to find this when gathering crops from the player's farm in Valley of the Four Winds.

[item=97986] ([quest=32853]): Chance to find this when gathering (not solving) Archeology fragments from Tol'vir dig sites only. You can also find it inside of a [item=87539].

[item=97990] ([quest=32859]): Can be bought from [npc=71226] near Razor Hill for 1 [item=97849] which is rewarded for completing the Weekly Quest [quest=32862]. Now has a chance to drop from level 90 mobs in the Northern Barrens.

[item=97981] ([quest=32843]): Can be fished up from pools in Pandria. This includes large pools that spawn during fish swarms.

[item=97983] ([quest=32847]): Earned after defeating Bruce. If you have already defeated him, you can buy [item=93823] from the merchant in the arena area.

[item=97985] ([quest=32851]): Chance to receive this when opening [item=86623] for completing Blingtron 4000 from [item=87214].

[item=97979] ([quest=32839]): Can be looted from [item=97954] found around overturned Caravans or for protecting a Caravan in transit during the Darkspear Rebellion going on in Norther Barrens. Has a chance to be inside of [item=92813] earned from running Random Scenarios.

[item=97987] ([quest=32855]): Found inside of [item=93724], which is rewarded for doing He Shoots, He Scores!, It's Hammer Time, Target: Turtle, The Humanoid Cannonball, and Tonk Commander at the Darkmoon Faire.

Defeating each of these new champions will earn players the Achievement Deck Your Collection (Season 1).

For anyone wondering, yes this is still obtainable in WoD.

The items' sources are all still the same as 5.4.8's, apart from:

[item=97979] now comes as a drop from mobs in Socrethar's Rise in Shadowmoon Valley, Draenor. For example [npc=84888].

[item=97982] also is now a drop, but from [npc=78259] in Gorgrond (start at roughly 56.6, 52.0 where a path leads to their cave).

Finally, it's also worth noting that [item=97985] is now obtainable from Blingtron 5000.