GW2. A guide to the Cosmic Observatory Strike Mission from Secrets of the Obscure.
Getting There
Find the Cosmic Observatory by using the Strike Mission portal only accessible in the Wizard’s Tower of the Secrets of the Obscure expansion area. In the LFG, groups may be forming advertising it as “CO” or “SotO”.
Boss Mechanics
Shooting Star – The player with the lowest health will be targeted with a Green Arrow. This will follow them wherever they go and will result in an attack that deals heavy damage and apply a healing reduction debuff. To mitigate this, the squad must stack at least 5 players together on the targeted player so they can share the damage. The healing debuff also does not occur if enough are stacked together. Make sure that the targeted player stands clearly further back than the rest of the squad so that it travels through them before it hits the target.
Spinning Nebula – Dagda will spin around, shooting out projectiles and creating a damaging area around her. The projectiles can be body blocked by pets, but moving away from the boss during this time is a good idea anyway because of the damaging field. If Dagda moves during this, there isn’t a need to follow since she will return back to the center shortly.
Orange Circles – The seven closest players to Dagda will have an orange circle appear beneath them. Before hose circles fully fill, players should spread them out so that the damage does not stack.
Demonic Blast – At 90%, 75%, 50%, and 25%, there will be multiple red cones in a spiral. Being hit by these cones will grant three stacks of Residual Anxiety (explained later) and a weakness debuff that reduces your damage dealt by 25% which lasts 3 minutes and cannot be cleansed.
As well as the Demonic Blast attack, every 25% the boss will also push all players away and create a deadly red area in the center of the room. The boss cannot be targeted and this red area will persist until you kill all the demons called “The Tormented.” Dodge out towards the edge of the platform and regroup with your allies to take out the demons. Once finished with this mechanic, a new phase with new mechanics will begin.
Soul Feast – Periodically a demonic entity will spawn and fixate toward a player, which they can see by the bullseye above their head. Players standing beside this Soul Feast will gain stacks of Residual Anxiety over time. Whoever the Soul Feast is targeting needs to move out of the group to lure it away from their allies. Then other players need to pick up the lights that spawn on the ground with the red hand icon over them, and use the Special Action Key “Purifying Light” while targeting the Soul Feast to destroy it.
Residual Anxiety – is a debuff you gain which lasts for 3 minutes and stacks up to 10. You get stacks of this debuff when getting hit by specific mechanics of the encounter (Soul Feast and Demonic Blast). When you reach 10 stacks you will be mind-controlled, becoming hostile to your squad and being taunted, causing you to lose control of your character. If this happens, your team may attack you to put you in the downed state, resetting your hostility and anxiety stacks.
Planet Crash – The room will fill with a blinding light while Dagda gains a break bar. If the break bar is not broken before the attack finishes, she will send a spirit bomb which will deal massive damage to your squad. Breaking the bar will diminish the effect of the attack greatly.
Meteor Shower – Dagda channels a spell which covers half of the platform. Move to the other side.
Strategy
Sticking together with your squad is important for almost every part of this fight, but there is one mechanic that can punish sticking together too tightly, and it’s the Soul Feast. It can give stacks of Residual Anxiety to your whole squad and this can be further complicated if the boss enters a new phase and a Soul Feast is still alive. So the Soul Feast is the most important mechanic to watch out for. Be proactive to pick up the Purifying Light and throw it at the Soul Feast as soon as possible. DPS players should prioritize doing this to minimize the disruption to the group’s synergy.
Otherwise, be prepared for the phase changes at every 25% of the boss’s health where you’ll need to get out of the center of the room quickly. During this time you also need to avoid the Demonic Blast cones so you don’t end up getting a huge damage debuff for 3 minutes. CC the break bars when they appear, and they will be very obvious since you won’t be able to see anything else.
Credit to Vallun for the video.Challenge Mode
The difference between Normal and Challenge Mode of this strike mission is that there is a relevant enrage timer. There is a 10 minute time limit, and many of the mechanics of this encounter will decrease the damage you deal or make it difficult to use your attacks on the boss. For example:
- The Spinning Nebula projectiles will now apply a debuff that reduces damage dealt significantly and will stack up per projectile that hits you.
- Dagda gains Demonic Resistance periodically which reduces all damage heavily and must be removed with the special action key ability.
- Orange Circles occur often, forcing players to leave melee range or the vicinity of allies that can buff them.
- More Soul Feasts spawn, which can mind control players and waste your time having to knock them back to their senses.
Besides those, most other mechanics are just more punishing, like failing to break the CC bar will result in a full wipe instead of just a massive hit. It is suggested to take Ranged DPS because of how much splitting you have to do and areas you have to avoid.
Demonic Resistance – Throughout the fight, Dagda will gain a buff that greatly reduces damage taken. Also throughout the fight there will be lights that drop on the floor. Pick these up and use the Special Action Key ability while targeting her to remove 5 stacks so this must be done twice to remove her buff and allow players to fully deal damage. This will last about 20 seconds before you need to remove the stacks again. You can see the purple icon with a broken shield on it which will blink when the buff is almost up again.
The light will only last on the floor for so long, and timing may require you to use them later when they have already disappeared, so it is a good idea to preemptively pick up the lights on the floor especially if they have been there for a while. The Special Action Key abilities will only be available 15 seconds after you pick them up, but it will still extend their usable duration.
Spinning Nebula – While this mechanic is generally the same as normal mode, it grants a stacking damage dampening debuff. You don’t want to be hit by any of these projectiles especially as a DPS player. Healers should step in front to body block any projectiles from reaching their DPS players. Minions can also block the projectiles. The further you move away from the boss, the more space you have to get in between and avoid the projectiles.
Soul Feasts – These pinkish areas on the ground will fixate and chase one player while pulsing the debuff Residual Anxiety to players inside them, and at 10 stacks of this debuff you will become mind controlled until allies knock you into downed state. While Soul Feasts can be destroyed with the Special Action Key ability, there are so many of them that it may be inefficient to try to clear them all. The fixated player may just want to run away until they despawn.
Roman Numerals – Like the Kaineng Overlook Minister Li mechanic, Dagda will also spawn roman numerals above players heads to predict an attack. The order in which she attacks them is defined by the numbers (I, II, III, IV). These players must spread out because if the attack hits any players in between them and the boss, it will kill them. If they are the only ones damaged, it will NOT be lethal damage.
Green Circles – Two of these will spawn and at least three players must be in each circle to prevent your squad from being nuked. These can be stacked together with at least six players, but who counts for each green circle can be unreliable so splitting them up slightly may be safer.
These mechanics by themselves can seem easy to handle, but when they overlap things can get complex and dangerous. Getting the lights on the ground early will allow you more time when you need to stack for Greens Circles or split for Orange Circles. Also remember that at 75%, 50%, and 25% the boss phases and you need to evacuate the center, so delaying DPS around these times may be useful to avoid stacking mechanics.
Credit to GilGalad Gaming for the video.Achievements
Cosmic Observatory Strike Mission – 5AP – 1MP 
Complete the Cosmic Observatory strike on normal difficulty.
Legendary Cosmic Observatory Strike Mission – 5AP
Complete the Cosmic Observatory strike on challenge mode.
Danced with the Stars – 5AP
Complete Challenge Mode without being hit by the Spinning Nebula attack. This is when she ports away, spins and creates many projectiles. Always move as far away to maximize the space you have to avoid these, or quickly move behind the boss where the projectiles aren’t aimed at.
Precision Anxiety – 5AP 
Mind Flayer
Complete Challenge Mode with all players having been possessed exactly one time and surviving. This is done by standing next to the Soul Feasts to continually get the stacks of debuff.
This can be done in a controlled manner where a few players get mind controlled at a time and next to each other so that others can quickly knock some sense into them. This can delay the fight quite a bit because it forces you to stop DPS and to fail mechanics, so perfecting the rest of the fight is that much more important.
