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Note: The king must stay alive, otherwise you lose the mission. Make sure that the healers in your party give precedence to healing him. This mission is the only way to get to the Ring of Fire Islands, where the skill trainer with all non-elite Prophecies skills, Dakk, can be found, and where many elite skills can be captured. This means that it is important for any player seeking to unlock skills to complete this mission. Unfortunately, it also means that there are many players being run to this mission directly from Beacon's Perch through Droknar's Forge. These players do not have infused armor and do not know about it. Make sure to confirm all your party members are infused, or they will melt before the Mursaat.

Preparation
Lack of teamwork is the primary cause of failure on this mission. Make the following decisions before heading out:

Determine which party member will talk to King Jalis Ironhammer at the start of the mission. The king will follow whomever first talks to him, but will run into the fray if he gets too close to an enemy. To increase the king's survivability, a caster should talk to him and try to stay out of the frontlines. Later, when the king opens the gates to the keep, he will start following whomever is closest to him when the gates open. Everyone but the king's babysitter should stay away from him at this time.

Agree on the defensive strategy to be used during the siege of the keep (see below).

Decide who will lead the party and call targets.

This mission has lots of Summit Giant Herders and Giants that can knock you down. Warriors should carry skills such as Balanced Stance. Remember that Giant Stomp is a skill (but not a spell) that can be interrupted. As a general guideline, consider bringing at least one dedicated interrupter; well-placed interruptions will considerably ease the difficulty of defending the fort during the siege.

Here are some additional tips on party formation:

Bring at least one warrior who can soak up damage and keep the enemy warriors (especially the Jade Armors) busy.

Bring three to four ranged offensive units (spellcasters or rangers). They will be the primary damage-dealers.

Trappers are very effective in defending the fort during the siege. Traps at the two entrances hinder the enemy's movement, which also helps the tanks keep aggro. Placing traps on the bridge above the gates will still hit anything attempting to enter, while also keeping the ranger somewhat shielded from direct melee attacks.

Shutdown Mesmers and mesmers with degenerative and interrupting skills are very useful against Mursaat spellcasters. Interrupt the Chain Lightning of Mursaat Elementalists, and divert the Orisons of Healing of Mursaat Monks. Keep an eye out for Mark of Protection and shatter them. Shatter Hex on your hexed tanks can also be immensely effective, because of the preponderance of enemy mesmers and necromancers.

Minion Masters are useful in the first part of this mission, but are less useful during the siege, as Jade Armors and Bows do not leave exploitable corpses. Corpses will be available, but fewer than in the earlier parts.

Reaching City Gates
The first portion of this mission is very manageable if care is taken not to aggro multiple groups at once. Begin by speaking to King Jalis Ironhammer to have him follow your party (point A).

You will first encounter a group of three Stone Summit Beastmasters patrolling directly ahead of where you enter the mission. Kill them and then head up to the right. Circle counter-clockwise around the peak, and attack the Ice Golems standing atop it; this will avoid having to fight the Stone Summit on the left rear side of the peak while Ice Golems are firing down on you. Kill the Stone Summit group next and then head across the bridge. At the other end of this bridge is a stationary group. A second group patrols the ridge behind this group, and is usually heading towards the first group when the party approaches. As it is not advisable to take on both groups at once, you have two choices: wait until the patrolling group comes down, turns around and heads back up the hill, or use someone to quickly pull the stationary group out onto the bridge to handle them there. The bridge itself provides a narrow choke point, so is an excellent place for rangers to lay traps. A random boss will spawn on the ridge too, providing an elite skill.

The path from the ridge leads down to the front gates of the city.

Clearing City and Fort
Here is the first objective: clear out the eight groups of foes in the city. As with the previous section, this part is not difficult if the party is careful not to aggro multiple groups.

After completing this objective, lead the king to the right-hand side of the wall (point B). There is a gate here—lead him to it and he will open it for you. However, be careful with the king: he will start following whomever is closest to him when the gates open.

Three groups reside in various parts of the area behind the wall: one on the far battlements, one in the center and one coming down off the hill on the far side. If you time this right without charging in, you should only have to fight one group at a time. If the party has a sufficient number of ranged attackers, they can attack these groups from below the wall. Often, the enemies here will not stand close enough to the battlements to return fire, making it very easy to eliminate them. Either way, once you've cleared out this area, head up the path on the far side.

From here, the path leads around to the right, and into the fort. Again, take your time. There are several groups containing Stone Summit Gnashers, who will attempt to use any corpses to create minions. A good counter-strategy for a Necromancer is to quickly cast Well of Blood when a body drops, even if the party doesn't need it, as it can be cast quicker than the Gnashers' Animate Bone Fiend spell. All these groups are stationary and should be taken out one at a time.

Note: There is a small promontory at the top of a hill before encountering the Stone Summit Gnashers. A player with a Longbow or Flatbow standing here can sometimes shoot Dagnar Stonepate and lure him from the courtyard back to the party, where he can be easily killed. This makes clearing out the fort a bit easier.

Once you reach the east wall of the fort (where the two ballistae are), descend the steps to the courtyard, and hug the east wall. Leave Dagnar (for now) and instead wipe out the east stationary group. Go up the other stairs on this side and kill the remaining groups, one at a time, until the fort is clear; this completes the second objective. Then, fire the west wall's ballista at the group of giants foolishly standing out there; otherwise, you'll have to fight them later. During all of this, the party member the king is following should make a special effort to stay far enough away from the fighting, as he has a tendency to run into the middle of the melee. Finally, kill Dagnar.

Holding the Fort
During the cut scene Vizier Khilbron appears and summons a few Smoke Phantoms to aid you (five: two on one fort entrance and three on the other) and the king settles down onto his throne, leaving the fighting to you. You must now defend the fort against numerous random groups of Enslaved Frost Giants, White Mantle, Mursaat and Jade Bows/Jade Armors.

The siege consists of three phases. During the first phase, the waves consist of Stone Summit Dwarves and Enslaved Frost Giants, and includes one of six golem and Stone Summit Dwarf bosses. During the second phase, the waves consist of Mursaat and jade constructs, as well as one Mursaat or jade construct boss. During the third phase, the waves consist of White Mantle members, there is no boss during this wave, but the final wave is a large group including Confessor Dorian.

Make sure that the east and west walls are each manned by a party member, preferably a Ranger or caster. These players have three tasks:

Watch their side of the wall and warn the party when the enemy groups start their approach.

Operate the ballistae as needed. The attacking forces will often pause in a ballista's target area, and can be killed or weakened before they get near the fort.

Use their ranged attacks as the enemies get within range.

Tip: This is optional with Strategy B because enemies have the time to regain all health before fighting the party.

There are three common strategies for holding the fort:

Strategy A: Guarding the Gates
The rest of the party should split into two groups, one guarding each gate. Ideally, a Monk will be in each of these groups, providing healing and maintained enchantments, also he could fire the siege weapons when the enemies walk to the portal doing huge damage even before they get to the gate. Heal the phantoms as well, if possible. As tempting as it may be, don't stray too far from the fort to attack a group that has stopped outside. If you become too divided, the enemies will overwhelm you.

The enemy groups will usually assault alternating sides, but not always. If one side is starting to get overwhelmed, the group covering the other side should be able to run over there to support them and have time to get back. If both sides are having problems, the groups should retreat to the center of the fort and continue fighting together. Warriors should consider using a movement speed boosting skill. This allows them to run quickly from one side of the courtyard to the other as needed.

The most challenging group is the one led by the Mursaat Boss, flanked with Jade Armor/Bows. This mob requires a significant amount of damage to defeat; unless everyone is attacking in unison, the Mursaat will stack up and overpower your group. It is recommended to leave the boss last as taking him down is much slower than killing the weaker enemies around him. Make sure no Mursaat or Jade break through to King Ironhammer: he doesn't have infused armor and will die quickly if they attack him.

Strategy B: Guard the King
Probably the best strategy for completing the mission. The entire party should stand at the king's throne in the area at the top of the stairs, and wait for the enemy to come to them. Do not leave the king for any reason. This strategy requires much less coordination to execute successfully compared to watching over two gates. As soon as an enemy group makes it inside the gate, attack them when they come up the stairs or catwalks that lead to the throne area. Do not get lured down the stairs to go chasing after the next target: if you die in the courtyard, it will be very difficult for the rest of your team to resurrect you until the current wave is over, potentially costing the team the mission.

Priority should be given to the attackers that pose the greatest threat to the king: first eliminate the Jade and Mursaat, then White Mantle, and finally any bosses. The only exception to this order should be if a priest or healer is impeding the elimination of an otherwise higher-priority foe. Because more enemies may arrive during a fight, constantly reassess which of the targets at or near the top of the stairs has the highest priority. A single person should be designated to call targets.

Note: While camping near the throne, King Jalis Ironhammer will occasionally wander forward nearer to the stairs. If this happens simply position yourself around him so that incoming enemies will attack your party first.

When defending the fortress with henchmen stay next to the king and wait for enemies to approach you. Never aggro an enemy until it attempts to go up the stairs leading to you; many times Jade Armor and Jade Bows will start fighting with other enemy units which will aid you greatly.

Strategy C: Counterattack
This strategy begins similarly to strategy B. The party initiates the bonus by lighting the torches, then defends near the king's throne. However, after the initial several waves of attacks, there is a break in the battle. At this point, the entire party heads outside of the gates and proceeds north, ensuring that no creatures were already en route to the keep from either the east or the west. While heading north, you can safely ignore any Mursaat and Jade that are in the Dwarven villages, if any. They are related to the bonus, and if the bonus had been taken they would have been part of one of the first few waves to attack the fort.

All enemies that attack from this point onward spawn in an area to the north of the keep near the portal that later transports everyone to Ember Light Camp. To reach the keep from the spawn point, all enemies must pass through a narrow choke point (point D). The party members can station themselves at the choke point and eliminate all the attackers without risking the King engaging any of them. Dorian's party also spawns at this location and can be eliminated in the same way.

Note: Just below the choke point are two parties of Jade. These can optionally be ignored, or killed during breaks in the spawns so that risk of accidentally aggroing them is eliminated.

Note: the portal only works in the cutscene. Walking through it prior to completing the Thunderhead Keep mission will have no effect.

An important tip
Taking the bonus of the mission might actually make the mission easier. The bonus Jade Armor and Bows will attack the fort first. If your party stands behind King Jalis in the fort, the Jades will stop on the courtyard, attacking any enemies coming in from the gates. They will easily wipe out all of the Stone Summit as they do not have infused armor. However, if you're unlucky, a group of Stone Summits may get past the Jades if the Jades are too far away from the gate. Dispatch of these groups as fast as you can and be careful not to aggro the Jades. The Jades will also kill some of the attacking Mursaat and White Mantle. When the defending Jades are wiped out, continue defending the fort with strategy A or B.

Killing Confessor Dorian
The last group to attack is Confessor Dorian and his group of White Mantle. They will appear on the eastern side, but will enter at the west gate. When this group is spotted, everyone can leave their assignments and engage the group together at the west gate. After he is defeated, collect any drops in and around the Keep, then talk to the king.

Tip: After defeating Confessor Dorian, if party members go outside of the Keep to collect drops, always keep at least one person inside the Keep. Additional Jade and Mursaat are in the foothills around the Keep. If they wipe out the rest of the party, the member who stayed in the Keep can still talk to the king to complete the mission.

Tip: While Confessor Dorian's group is approaching, they will stop for a few seconds on the spot where the shots fired from the Western artillery pieces land if activated. This is an easy way to take out a few White Mantle, making the job of killing Dorian that much easier.

Tip: Confessor Dorian's group can be easily destroyed with enough ranged attackers in the party. When they spawn, they're going to move behind the small tower where the king is staying. With a longbow, you can pull them towards the tower, avoiding melee contact, thus eliminating them with ease. Sometimes, one of the accompanying White Mantle might run in the opposite direction, outside your radar's range. If you wait a few seconds, he will eventually come back and follow his usual route.

Bonus
The bonus is to save the dwarven soldiers outside the keep by lighting the Storm Beacons to draw the Mursaat forces on the outskirts of the keep to the keep.

After clearing the fort and watching the cutscene (right before the siege), the king will ask you to light the beacons to save the Dwarves trapped outside the walls. Lighting the beacons will draw the groups of Mursaat on the outskirts of the keep to the fort. Specifically, each beacon lit early enough will attract two Jade Armors and one Jade Bow to the respective gate.

There are two Storm Beacons that you must light: one on the east wall and one on the west wall (both points marked 1 on the map). Enchanted torches appear at the base of each, so it is just a matter of running to each beacon, picking up the torch there and clicking the beacon. You have only a few seconds after the cut scene to do this, so it'll be easiest to designate one person on the team to light each beacon before taking their assigned position. However, it is still possible to light both beacons with one person (for full hench parties), as long as you drop the torch when running from the first beacon to the second.

The dwarves outside the keep will plead for their lives, if they scream out "The end is here! Great Dwarf save us!" then the chance to light the beacons is lost.

The credit for the bonus is only granted by talking to the King after killing Confessor Dorian's group at the end of the mission. You can use this time to pick up any unclaimed items or to explore the area outside the fort.

Tip: The 6 additional Jade enemies that come forward as a result of the beacons are hostile to ALL the other enemy units, including other Mursaat, Jade, and White Mantle. If the entire party huddles around the king's position, it is possible to not aggro them. When the enemy waves start coming in, these additional enemies can provide a first line of defense. Sit back and watch as they tear through the Stone Summit with Spectral Agony.

Note: Normally you have to light the beacons before the waves start coming; however, on some occasions there will be a bug that allows the bonus to complete while lighting the torches too late. It is unknown what causes this bug to trigger. Sometimes lighting the torches on time also results in a failed bonus.