ENCOUNTER 2: LORD JARAXXUS
Story time! Once you've finished off the menagerie, Tirion invites a special guest to summon in the next combatant. This is transcribed from audio files in the latest PTR patch.
Tirion Fordring: Grand Warlock Wilfred Fizzlebang will summon forth your next challenge! Stand by for his entry!
Wilfred Fizzlebang: Thank you, Highlord! Now, challengers, I will begin the ritual of summoning! When I'm done, a fearsome Doomguard will appear!
Wilfred Fizzlebang: Prepare for oblivion!
(A demonic shape appears.)
Wilfred Fizzlebang: Ah ha! I've done it! Behold the absolute power of Wilfred Fizzlebang, master summoner! You will bow to me, demon!
(The shape coalesces into the form of an eredar. The bad kind, not the space Russian kind.)
Lord Jaraxxus: Trifling gnome! Your arrogance will be your undoing!
(Jaraxxus instagibs Wilfred Fizzlebang.)
Garrosh Hellscream: Treacherous Alliance dogs! You summon a demon lord against warriors of the Horde?! Your deaths will be swift!
King Varian Wrynn: The Alliance doesn't need the help of a demon lord to deal with Horde filth! Come, pig!
Tirion Fordring: Everyone, calm down! Compose yourselves! There is no conspiracy at play here. The warlock acted on his own volition, outside of influences from the Alliance. The tournament must go on! Quickly, heroes, destroy the demon lord before it can open a portal to its twisted, demonic realm!
Not quite the Doomguard we were expecting, but it'll do!
Jaraxxus deals in all kinds of fire, as you'd expect. One of his combos involves Incinerate Flesh:
Incinerate Flesh -- Burns the flesh off your bones! Absorbs the next 30000 healing received and decreases damage dealt by 50% for 15 sec. If Incinerate Flesh is not removed before it expires it will cause a Burning Inferno.
Which will spawn a Burning Inferno if not healed through completely:
Burning Inferno -- The Burning Inferno caused by Incinerate Flesh not being removed inflicts 3120 to 3280 Fire damage every 1 sec for 5 sec to all friendly targets.
He also appears to target players with Legion Flame and place fire patches on the ground where they were standing:
Legion Flame -- Burns the target, causing a Legion Flame to appear at the targets location every 1 sec for 6 sec. The Patch of Fire spawned inflicts 3900 to 4100 Fire damage every 1 sec.
And of course, the old eredar standby of infernals. We sure love infernals. Almost as much as we love poison clouds.
Infernal Eruption -- Lord Jaraxxus summons an Infernal Volcano which causes Infernals to spawn.
Infernal Eruption -- Summons a Infernal and inflicts 9263 to 9737 Fire damage to targets in a 10 yard radius.
As if those weren't enough, he also does an AOE DOT...
Touch of Jaraxxus -- The Touch of Jaraxxus inflicts 3900 to 4100 Shadow damage for 12 sec and causes nearby players to be effected by Curse of the Nether.
Curse of the Nether -- Inflicts 4388 to 4612 Shadow damage every 1 sec for 15 sec.
... and summons in an add. I'm not sure how she works. There's a spell for him to summon a Nether Portal, which you may need to stop from happening to prevent her from spawning.
Spinning Pain Spike -- Mistress of Pain sets her sight on an enemy inflicting Physical damage.
Mistress' Kiss -- Next spell cast interupts that school for 8 sec and causes 8288 to 8712 Shadow damage.
Shivan Slash -- A whirling attack that deals 50% weapon damage and pierces through armor.
So, don't stand in fire, don't spawn a fire, don't be near fire, if you get engulfed in fire get healed through it. Also, fire.
Once you defeat Jaraxxus, it's time to face off against Tirion's next challenge!
ENCOUNTER 3: THE ENEMY CHAMPIONS
Tirion announces the next battle, saying that you are to face his best knights. Then things get a little more complicated. If you're Horde, Varian takes offense to Garrosh's accusation that Jaraxxus was an Alliance trick to kill Horde members and demands that Tirion allow the Alliance champions to fight in place of his knights. If you're Alliance, the situation is the same but with Garrosh being a big baby instead and offering Horde champions.
Tirion reluctantly agrees. And then your faction leader either hops in with you or cheers you on from the sidelines -- it's dificult to tell from the sound files whether Varian/Garrosh are in the thick of it with you or just futzing around in the bleachers. (Comedy gold from the sound files: Varian calling the Horde champion you just killed a "worthless scrub".)
As stated in my 5-man roundup, I don't have information on the various Champions other than their names.
Ultimately, though, you end up killing the other faction's Champions, and Tirion is disappointed and angry over the loss of life for such a petty squabble.
Tirion Fordring: A shallow and tragic victory. We are weaker as a whole from the losses suffered today. Who but the Lich King could benefit from such foolishness? Great warriors have lost their lives, and for what? The true threat looms ahead, and the Lich King awaits us all in death.