Grand Stairs Guide
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This is a pretty simple instance do do the hardmode on. There are two factors that determine if you finish it on hardmode, the first being that you activate the second boss withing 10 min of the first boss and the second that you do not kill the devoted add on the last boss.
Boss One
You will start by going down a long staircase towards the first boss. You are cut off from him by a raised drawbridge at first. The fellowship should stay on the final landing of the staircase while a hunter or mini approaches the bridge and waits for the boss to do his speech. Once he is finished, the drawbridge will lower and he will attack. He will flash some more text about something and from that moment on, you have ten minutes to activate the second boss. Once he is finished his little spiel, DF or feign death. This will reset him but will not close the bridge. The fellowship can now proceed down the stairs to your left in the first boss room.
Boss Two
You are on a timer now, so speed is of the essence. When you reach the next platform at the bottom of the stairs, you will be attacked by 2 warg riders. Mezz one and take the other one out quick, then move onto the messed one. Continue forward to the next set of stairs. There are two stealthed goblins at the top of the stairs. Take them out quick following the same method and move down the stairs. You will be attacked by two warg riders again at the bottom of the stairs. Use the same method to take them out.
You should now be on a platform with 3 mobs in front of a raised drawbridge to your right and a long set of stairs to your left where the wargs you just fought came from. Its time for the suicide run! The best combo is a guard and champ, but just about any heavy can do it with some help. DO NOT apply any heal over times to the runners as it will draw the aggro of everything they are running through back onto the fellowship. The runners will proceed down the stairs, turn right, and go down some more stairs to a platform filled with warg riders. they will hang a right and go across a bridge to another platform and then up some stairs. At the top of the stairs is the second boss platform. Whoever is left standing will hang a left once they reach this platform and run up the stairs to the boss. keep running off the end of the stairs (this is the suicide part) and fall to your death below. This should activate the second boss, stopping your 10 minute timer and lower the drawbridge the rest of the fellowship is standing by. The boss will reset since he has no one to aggro on now.
You are now free to take out the 3 mobs guarding the bridge. I recommend CC everything but ranged. If one of the melee mobs breaks through or resists, just have a guard or champ tank it while everyone else focuses on the ranged. Once all three are down you can move onto the three patrolling behind the bridge. Use the same CC technique as the previous mobs and move on down the stairs.
You should stop at the landing in the middle of the stairs. In front of you is the platform with the second boss. Directly in front of you at the bottom of the stairs is the same batch of 3 mobs. To the right by the closed gate is another group of three and by the suicide stairs is another group of three plus the second boss. You will want to use the same method as before to pull the groups one at a time starting with the ones at the bottom of the stairs in front of you, then the ones by the gate. Fight them from the landing on the stairs you stopped at. This is the reset point for the boss, so if comes with the last group that he is standing with, he will reset and leave you to fight the last group of three.
Once you have burned the three groups down, make your way to the closed gate. This is where you want to fight the boss. He has a knock back that at best will send you off the platform to your death and at worst send you flying down to the wargs your heavies ran through before. The fight is a simple tank'n'spank Anyone who does not need to be melee should stay by the right corner of the gate while the melee should tank the boss in the left. Once he is down, loot the two chests and head back yo to the platform with the first boss.
Boss Three
When you come back up the stairs to the first boss platform, you now have the option of going right across a bridge that was previously raised. You will encounter similar groups of 3 mobs once again. This time you will want to cc the ones on the left and right and take the big guy in the center first. The other two mobs are healers, so make sure if one breaks free he gets clobbered or otherwise interrupted. There will be two ranged mobs patrolling this area as well but they can be taken on by themselves between fights.
Once you make your way through a few groups you will come to another staircase (they don't call it the grand stair for nothing!). Just beyond the top of the stairs is a group of 3 healers and to melee mobs. do whatever you can to only have to deal with one melee and one healer at a time. If your group can mezz everything but one at a time, great, but usually you will have to make due. It can be a tough fight if the healers are not kept in check, but you should have little trouble.
The room in front of you is the third and final boss. There are two sets of flags just beyond the top of the stairs. Group up in the middle of the flags. You will have the boss to fight, and his whipping boy, a mob called the devoted. The devoted is phase two of hardmode. If the devoted dies, you fail hardmode. So, you do not want to attack the devoted at all. He will randomly attack people and is immune to all forms of CC, so don't even bother. If he takes any damage or you try and affect him with any skill, even non damaging ones, he will summon two ranged adds. So make sure you take off any damage reflecting items you have, any pets are put on passive (sorry LM' no cats for this fight) and do not AoE or use any damage reflecting skills during the fight.
If things do get out of hand, you can run the boss back down the stairs you just came up to reset his room, including the devoted and any adds he may spawn.
Now, as a group, you will all run through the throne room to the closed gate behind the boss. Be sure to jump at the raised platform and stand as a group in the center of the gate. The devoted will have spawned near the top of the stairs where you entered from and will run to your group and randomly attack you all. Do nothing. He will eventually spawn his two ranged mobs automatically, but behind the closed gate. Once he does this, you can go and engage the boss.
The boss fight is a long one, so if you get any CJ's early, its best to give him some yellows. The fight is basically going to be one person running around with the boss aggro'd on them while everyone else attacks the boss. Once someone else gains aggro, its their turn to run around. This works best with two hunters as they can ping-pong him back and fourth, but any combo should work. Every now and then the boss will apply a massive armor debuff wound, so have your wound pots ready. he will also drop puddle of fire occasionally. Try not to stand in it or run through it, it hurts, a lot. After you take the boss down about half way, he will do an AoE attack that hits for around 1700 moral and stuns for about 2s. be ready to down a heal pot ASAP. He will continue this behaviour until defeated. At that point, the devoted will run away and the gate with the two trapped ranged mobs will open, freeing the ranged mobs. They too will disappear, but not before they pepper the mini with pew pew, so its advisable for the mini to feign death while everyone else gets a few swings in before the disappear.
Woot! you just finished phase two and completed the instance in hard mode!
Now its time to sit back and enjoy the fruits of your labor! There should be 5 chests to loot now. They will contain a mix of heritage runes, sealed settings, a trophy item, some nice purple or teal gear, and two coins. One is for the radiance boots, the other is the non radiance boots. The radiance coin can be traded in at your class trainer in the 21st hall, while the other can be traded in at orc-watch.
For a first run, expect to take about an hour to finally complete it. You will have a lot of "learning experiences" so don't worry about it. With a dps heavy group who has made the run a few times, you can expect to finish it all up in about 20-30 min per run. Each chest you loot (including the second bosses) each drop enough coin to net each player about 80 silver per chest, which should more than pay for the suicide squad's repair bills.
To run the instance again, simply exit out of the open gate behind the throne, disband the group and start the invites again!
Source: http://council-of-eriador.com/coeforum/index.php?action=printpage;topic=1680.0