The Second Rule of Brawler's Guild (Season 2)

Brawler's Guild Fight Order (updated for 6.0)

note: all the bosses are the same as in mists, but the order is now different.

Rank 1
Smash Hoofstomp
Akama
Sanoriak
Goredome

Rank 2
King Kulaka
Fran and Riddoh
Kirrawk
Dippy

Rank 3
Mazhareen
Ixx
Blat
Vian the Volatile

Rank 4
Tyson Sanders
Nibbleh
Meatball
Dominika the Illusionist

Rank 5
Big Badda Boom
Leper Gnome Quintet (one is [npc=67514])
Millie Watt
Bruce

Rank 6
Doctor FIST
Unguloxx
Yikkan Izu
Proboskus

Rank 7
Ahoo'ru
Battletron
Dark Summoner
Bo Bobble and Max Megablast

The Challenge Card System
After purchasing a challenge card (from an NPC found next to the one who sells pots), you can queue for a specific boss. This is a diversion from the rank progression and has its own separate achievement, Now You're Just Showing Off (Season 2).

Rank 1
[npc=67572]

Rank 2
[npc=67540]

Rank 3
[npc=67451]

Rank 4
[npc=67596]

Rank 5
[npc=68377]

Rank 6
[npc=70983]

Rank 7
[npc=70977]
[npc=67483]
[npc=67490] Freakin' laser beams!
[npc=67571]
[npc=70659]
[npc=67518]

The old system of discovery is still in place as well. Accessing these bosses requires going out into the world and "discovering" quest items that unlock them. Check the page for Deck Your Collection (Season 1) for sources. At this time, I'm not sure what ranks each boss requires.

[npc=70748] & [npc=70750], "The Lady and the Bear"
[npc=70740]
Dippy & [npc=70648]
[npc=70678]
[npc=61013]
[npc=71081]
[npc=70616]
[npc=71085]
[npc=70749]
[npc=70736]
[npc=70794]
[npc=70666]