Nexona is considered to be the hardest mob within Veeshan's Peak. Once you learn the encounter, it really is rather easy. I will explain one of the simpler ways to finish this mob off. There is more than one but out of all of the strategies out there, this one seems the easiest pull off.
First thing you need to do is setup 2 groups that will remain on Nexona for the entire duration of the fight. Your MT group and a secondary dps group.
The other two groups will be add groups as x2 adds will be coming constantly throughout the fight.
Shinies
Make sure your harvestors can see ALL SMALL PARTICLES FROM FAR AWAY!
There are 6 total shinies in this fight to keep an eye out for. 2 spawn just outside of Nexona's room, 2 spawn in the main room area (1 north side, 1 south side) and 2 spawn up top where Nexona sits but they spawn behind where the specimen's reside.
You will need to dedicated one FD'er (monk/bruiser) to the top section of the room harvesting nothing but the top shinies. Dedicate also one more person to harvesting the shinies in the lower tier of the main room. This person can be part of the dps group on adds but they need to be able to see all small particles. The shinies that spawn just outside in the hallway can be harvested by someone in the Nexona groups.
Now that you have your three people chosen to do this you are ready to pull Nexona, but first you need to split up your raid to take care of the specimens located throughout her Chamber. 2 up top, and 3 below.
This is where the part of the Nexona fight is extremely critical. Put both Nexona groups on the center specimen and set your tank just slightly off to the side of it. Now, your two other groups for the adds you should have placed at the top specimens. Your MT should be the first person to hit a specimen as Nexona will come immediately after him. Because your MT is off to the side she will path down the ramp. If your MT is near the center of the specimen she will fly down the middle and you will have little time to react.
DPS is paramount here. Your add groups must be able to output enough dps to drop their first specimen and move on to the next specimen below them and kill that one within 1 minute, otherwise you will be backed up on adds and you will lose.
If you dont have enough dps at first to do this, start leaving up Specimens. Try killing only 4 instead of all 5, or 3. All that changes is Nexona at 90% will heal herself to full if one specimen is up, then again at 85% if a second is left up and so on.
Practice getting the specimens down as quickly as possible. Now with that out of the way its time to pull Nexona. Again, have your MT hit the center specimen first and commence burning the specimens. When the Nexona groups are done with theirs you want the MT to grab Nexona and pull her out into the Hallway about halfway down before the hallway bends and position her so her body is across the hallway and she is looking at the wall. YOU DO NOT WANT ANYONE IN THE NEXONA GROUPS ON THE RAISED SIDES OF THE HALLWAY!!! If people are the adds have a chance at warping to the MT group. Stay on the floor.
If you dont get Nexona placed quickly enough she will do a frontal power drain because there is not enough DPS on her. A dirge's "Magnetic Note" and a Coercer's "Thought Snap" come in handy on the run to the hallway because they do infact prevent the power drain while your MT positions Nexona as long as she is flying. Commence burn on Nexona for the two Nexona Groups.
While your MT and Nexona groups are handling the dragon the add groups should be just about done with the specimens. Prepare for the adds now.
You should have your MT or someone in the Nexona groups looking for the emote when a Shiney is up. Nexona will say, "I feel the spirits growing...good". A shiney is up somewhere, this is where its gonna take crack communication. You need to harvest the shinies as soon as possible. Depending on your add group dps will determine how fast you can pull. Your add groups should remain near the center of the front of the main room. Harvest the shiny, they will be popping once every 30 seconds roughly. You want to try to aim to have the adds close to dead when the other shinies spawn so you can just have your harvester do it right away. If the shiney is up top your Brawler should FD right away because the adds do have a chance to aggro the harvester as well as randomly mem wiping. They should remain FD until their add is engaged or another shiney has spawned. If shinies spawn in the hallway someone from the Nexona groups harvest them. Your OT puller should never be farther than a bow pull away from any new shiney spawning near Nexona. The last thing you want is dead people in the Nexona groups.
Continue practicing this and get good at doing the shinies.
Nexona has some special abilities to watch out for. Necrotic Rot will tick massive Disease damage on you. But it seems to be limited to ONLY people on her DPS list who either attacked Nexona and then stopped for too long or reached too much overall DPS on Nexona. So as long as people in the add groups never hit Nexona, they shouldnt get Necrotic Rot. If the Nexona groups pace themselves and keep their overall group dps between 15k and 30k to be safe you will be fine. Just have Cure Pots ready and watch for the effect on you, you wont have much time to cure it before you die.
Nexona has a Magicial AE (need name) as well that does more damage the closer you are and much more dmg if you are in front of Nexona. Place your Nexona group members near the back legs of Nexona to prevent them from getting blasted too badly. Its not that bad really and the add groups will barely feel it.
If you get Nexona to 45% your doing extremely well and consider it a winning strategy. However, at 45% there is a little trick hidden up Nexona's sleeve in addition to the constant x2 adds. She will summon Drakes that will come from the middle pool. The drakes have a nasty knockback ability that wreaks havoc on the add groups. Most guilds will be unable to handle the drakes AND still do the x2 adds effectively. Many guilds send two chanters to perma mez the drakes as they spawn for the remainder of the fight. There is only 5 that will spawn. One will spawn, then another a few secs later... then the next three spawn rather quickly after eachother. If you can seperate the drakes and get one chanter to handle three and one just two drakes, the other chanter can go back and forth between mezzes and help out with any power issues or dps thats needed. but your chanters need to be on the same page. As long as the add groups dont lose focus on their shinies and kills, Nexona will drop for you.
Also, you want to MAKE SURE you know where the next shiney is at all times. You never want to have 2 or even 3 up at a time and not know which one spawned first. If you harvest a shiney out of order or have more than 3 spawn you will trigger a nasty AOE that will kill your raid. Also, if you do too much DPS on Nexona she will do a massive AOE that most guilds can not recover from.
Practice this strategy and good luck to you and your guild. Hopefully grats on Mythicals!