Guild Wars 2 Guide - [BWE3] Raid Guide by Kaelran

The first area consists of three miniboss "trash mobs" and one boss at the end. All of these pulse minor AOE damage while you are within 1500m of them.

Blue Guardian
Invulnerability Boon - The blue guardian is invulnerable to damage and conditions unless you remove this boon with a boon-removing skill. Thieves, Mesmers, Necromancers, Revenants and Engineers can all do this.

Big AOE - An orange circle will appear on the ground with the bright orange contracting to the center as a timer for the explosion. Everyone needs to stack inside the circle before the explosion or take high damage. This damage cannot be dodged but can be blocked. The pulsing AOE can remove aegis so you want to use it as late as possible if you plant on blocking the damage with it.

Floaty Blue Balls - There are blue balls that fly around. If they hit you you will take some damage. If they hit the Guardian he will gain the Invulnerability Boon again so try to body block any that would. You can jump over them to avoid them if you need to.

Green Guardian
Teleport AOE - The guardian will spawn circles on the ground. If you do not move out of them quickly you will take damage and be teleported away.

Red Guardian
Physical Immunity - The red guardian can only take condition damage.

Seekers - The red guardian will spawn enemies called "Seekers" that look like red lightning elementals. The seekers will damage you if you stand in the AOE circle around them. They can be knocked back or kited.

Unconfirmed - Killing a seeker next to the guardian will damage him. Although when we killed the red guardian it looked like the Seekers take no damage.

Vale Guardian
Finally the boss of the area. It seems like it has the big AOE from Blue, the teleport AOEs from Green and the seekers from Red. It may also have the immunity boon from blue but fighting it caused everyone in our squad to DC. At 50% HP it splits into the three miniboss guardians who each spawn in front of their respective pillar.

SOURCE