The collector is a new instance with 4 Encounters.
First encounter:
One Big Spirit "The Collected Essence" (lvl 300) with a bunch of small spirits.
The collected essence spirit can't be attacked while it is big. It becomes small and attackable when a small spirit dies. In sum, kill a small spirit, the big one becomes small.. do damage to this collected essence till it becomes big again, kill another small spirit till the collected essence becomes small again. repeat this process till it dies.
Second encounter:
Sister Botanicus (lvl 300)
You'll see a few 'plants' around this boss. These plants heal the Sister Botanicus if they life. To kill the sister it is needed to kill the plants.
( i think it has to do with the 'green' circle that goes around. I suspect that each time the green circle is at a spot where a plant is alive, that this will heal the sister botanicus)
Each time one of the plants dies it will pop 'cocoons' on players. These cocoons will stun that player for 10 seconds, unless the cocoon gets killed (by pets or a player that is not cooned). Cocoons don't do damage.
Third Encounter:
After killing the sister Botanicus, Immortal Guardians are spawned near three walls. There are also spirits around, just kill them when you are near those.
You are not supposed to kill these Guardians, for they are meant to 'bounce/knockback' you over the walls.
Look for the lowest spot in the wall (where the immortal guardian is standing in front). That will be the spot you want to be 'knocked over'.
Tactic, let one player do this at a time, others wait till the other one gets over. The player will first lure (use the q button

Do this for all three walls.
Fourth Encounter.
After these walls you'll encounter the Secretary (lvl 250), which is just a NPC to talk with, and will warp you to the final encounter "The Collector". One person needs to talk to him to activate a nano in all teammembers.
This nano activates a "knock-back-attack" in all players. This will allow you to knockback the mobs in the next encounter. Only one player + all Engineers / Nt's / Traders will be able to use the knockback attack:
The first player that uses the knockback attack will be the only player in the encounter that can use the knockback attack.
NT's, Traders and Engineers will have the knockback attack by default enabling them always to be able to use it in the encounter with the Collector.
When entering the place with the Collector. Nothing happens till the collector is attacked. look around, you'll see Two towers: one with a Red Fire, one with Blue fire.
I believe there are going to be three waves with Shades.
First wave contains one Red Shade and one Blue Shade. Purpose is: Knockback the Red Shade into the Blue Fire.
Knockback the Blue Shade into the Red Fire.
Second wave contains two red shades, two blue shades.
Third wave contains three red shades and three blue shades + 3 Plague Shades.
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At that point our collector only had 1/3 hp bar left. Only trouble my team died due to plague shades.
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I've been told that Crats can use their mezzes to mezz these shades, making this "basketball"-knockback encounter bit less difficult.