Invincible's Reins

For those of you un-aware of who Invincible is, he/she was Arthas' Mount when he was alive (as a Paladin). During the Scourge Invasion Event, the grave of Invincible in Tristfal Glades was opened, and can now be seen as simply an empty grave. Wowraid came out with a SS of Invincible a week or so ago, so there was a lot of speculation if Arthas would drop his Mount or not. What interests me the most is that this says "Arthas" Blizzard has always insisted that "Arthas" is simply "The Lich King", so what happens? Only time will tell, and of course, whoever gets World First Fall of The Lich King :D

EDIT3: 42 kills and the mount is mine!
The 6.0.2 patch made a lot of this data obsolete unfortunately. I'll leave it here for nostalgic purposes.

Soloed [npc=36597] on 25 Man Heroic for [item=50818] (Invincible's Reins) as a 539 BM Hunter with no legendary cloak. I tried with survival for good AoE to get the adds down, but I've found that the adds aren't even a problem unless you let them stack up without killing them.

Preparation: I used a Tenacity specced spirit beast, the extra Spirit Mend was needed greatly, especially in my gear. I HIGHLY recommend speccing into [spell=109212]. Agility food([spell=104275]), [item=49633], and [item=79257] isn't a must but certainly helps. A core hound pre-cast [spell=90355] couldn't hurt either. [spell=56833] and [spell=56829] are BOTH required. I also had [spell=20895], I wouldn't say it's required, but it HIGHLY recommended. He is able to be taunted after enrage if you don't have the DPS to beat enrage timer, but this is NOT recommended and is extremely hard, it is much better for you to wait until you have the gear/skill to beat enrage, which I'd say is about 525 ilvl.

Phase 1:(100%-70%): Arguably the hardest phase, have your pet tank [npc=36597] and adds on the edge of the platform. As usual, avoid [spell=73529] of course, and try to avoid getting aggro from adds so you can stay topped. The part that makes this phase hard, is the [spell=70541]. When he casts [spell=70337] on you, you must heal through it, but at that time you are unavoidably under 90%, and if you get hit by an infest while under 90% health, you may as well use [item=95566] or die, because it's basically a wipe. The trick to avoiding the Infests are the pillars, as the Infests can be Line of sighted. Whenever he casts [spell=70337], it's almost certain he'll cast [spell=70541] right afterwards, so periodically get out of line of sight using the pillars in the room before Infest finishes casting, and it will be avoided, and you can continue DPSing while still avoiding [spell=73529]. Unfortunately, the [spell=70337] cannot be Line of sighted. If you accidentally allow an Infest to hit you, you can use a Master Healing Potion quickly to get above 90% and that will work as well! (however you can only do this one time through the fight). Once he hits, 70%, he will push into phase 2, and you most likely will still have adds up.

Phase 2:(70%): Stay at the edge of the platform to avoid [spell=68981], you need to be at 90% or greater for next phase., don't worry about Lich king, just work on getting [npc=37698] and [npc=37695] down. You may kill the [npc=36701], however you WILL want to leave a few up during phase 3, as you need them in order to avoid the [npc=36609]. Kill the [npc=36633] ASAP, if you don't they will knock you back if you allow them to get to you. Phase 2 will end after about a minute. Note: The [npc=36701] have an ability called [spell=69242] which is a silence, so it can prevent you from using [spell=34026] and Mend Pet, but that shouldn't really be any problem.

Phase 3:(69%-40%): Make sure you are topped off in health for phase 3, as he continues to cast [spell=70541] during this phase, and there are no pillars to avoid them from. He doesn't cast [spell=70337] in this phase anymore, so as long as you get out of [spell=72762] ASAP and don't get aggro from extra [npc=36701]s and/or Lich king himself, you should be fine. You WILL want to use [spell=20736] every minute on a [npc=36701], as it will mark you as tank and the [npc=36609] in return will not pick you up. DPS the Lich king down to 40%. Remember: At any time if he casts infest on you and you are under 90% health, it's a wipe.

Phase 4:(40%): Once he is down to 40%, he will no longer cast [spell=70541], so it is safe to stand in the [spell=68981] and DPS the Lich King all you want. Don't get too greedy and die to the AoE though. He will spawn more Raging spirits, these don't really need to be killed and most likely just die to [spell=115939] over time anyways, just DPS lich king and kill [npc=36633] ASAP just like in phase 2. If you start losing a lot of health, go to the outer edge to get out of the Remorseless winter, and wait it out with Spirit Bond and Spirit beast heal, better to be safe than sorry. Phase 5 will start after about a minute.

Phase 5:(39%-10%): Don't worry about being topped off or using distracting shot on raging spirits, he will no longer cast Infest or spawn Valk'yr in this Phase. As long as you have the DPS to beat enrage timer, getting to this phase means you've basically already won. There are still a few drawbacks and things that may still wipe you however; As usual, get out defile ASAP, and once in a while he'll use an ability called [spell=73654], which will pull you into [item=36942] with [npc=36823]. You are stuck inside Frostmourne for 40 seconds, after which Terenas will pull you out. This is mostly just a hinder to DPS and will not wipe you, just be sure to kill the [npc=39190] inside if they start running for you. Once you are out of Frostmourne, The Lich King will spawn [npc=37799] and these you may mostly ignore, you will most likely be topped anyways due to Spirit Bond and Spirit beast heal anyways. He will most likely pull you into Frostmourne 2-3 times, once you get out its best to use CDs and DPS him as much as possible before he casts it again. Once he reaches 10% you've won.

Phase 6:(10%-0%): At 10% he casts [spell=72350], killing you (you may not be killed if you use [spell=19263]). Role-play will commence, after it is over, just DPS him down. No further explanation needed. Once he's dead, collect loot for your 1-2% chance at [item=50818], cry that it didn't drop, enjoy the cinematic, and do it all again next week.

EXTRA: Being epic and surviving [spell=72350]: I've played around with surviving this attack and can say that if you have over 1 million health, you'll survive (usually only if you have full SoO heroic gear) or if you have over 700k health, you CAN survive it if you use [spell=19263], as this reduces damage taken by 30%, and the attack does 1,000,000, you will only take 700k, thus surviving the attack (Probably need about 540 iLvl to have over 700k health with the buff (Alliance:[spell=73828] Horde:[spell=73822]).

Good luck to all the other Hunter Soloers looking to solo the Lich King on 25M Heroic for Invincible's Reins, and I hope this comment helped you!

Video of me soloing the fight: http://youtube.com/watch?v=7oQcDq38HH0
Video of me surviving [spell=72350]: http://www.youtube.com/watch?v=mManaCXPDEE

EDIT: 547 iLvl with [item=102248] and am now one-shotting this every week, 10 attempts so far but still no mount.
EDIT2: 560 iLvl and I can kill him in about 5 minutes (there was 10 minutes left on enrage) 31 kills, no mount yet)
Armory to my hunter: http://us.battle.net/wow/en/character/whisperwind/Scorpob/advanced
Feel free to ask me any questions in-game if you are having trouble, or have any questions about this fight, or any others in the instance, I currently have the entire [zone=4812] instance on solofarm (Solo all bosses on 10N, then go out and switch to 25H for Lich King) every week until I get [item=50818] :P

World first Invincible went to Tsukky of Paragon on Lightning's Blade-EU.