Welcome,
My name is Abuse, a former lancer turned warrior tank/dps which is going to try and give you everything you need for the next patch, dungeon-wise.
I did not participate in any of the action, I simply looked hard enough and watched every animation, indication, and player in the group, in order to know what should you do and when, I do not take any credit for filming the original videos the GIF's are taken from, I do take credit for putting all of this together, so I would appreciate a kind thank you ^_^.
The guide I will be posting today, will be the guide for "Bathysmal Rise", a new instance that will be coming in the upcoming expansion "Fate of Arun", its detailed, as far as youtube allowed me to, I did skip normal monsters fights, since its mostly tank & spank.
*Some gifs are converted into "gifv" automatically and can't be displayed on this forum, there is a link attached to the gif.*
Bathysmal Rise
1st boss: Turtle
-special mechanics:
1) Shell Artillery -
Indication: Boss goes inside his shell, and marks 2 circles on the ground.
What would happen: after a few seconds boss AOE's between the circles, Poison Artillery.
What to do: avoid being in those circles.

2) Poison Cave -
Indication: Boss will AOE a corner left to the entrance (rocks are stockpiled on the wall and enters the arena).
What would happen: A poison like smoke (greenish) will be there, if not handled in time, the whole arena would be poisoned for a second, IT IS Cleansable.
What to do: a dps, or a healer (in the videos, its a healer) goes to the hole and closes it, if he missed a window,
its still doable after cleansing everybody. (window = chance to close it before it explodes on the arena).
Link: http://i.imgur.com/ufVpuD6.gifv
3) Adds -
Indication: Boss will have purple (purple/blueish) smoke coming out of him.
What would happen: Boss is going to summon adds.
What to do: Knock the boss down, stagger maybe works as well (didn't see a stagger in any video).
Link: http://i.imgur.com/XjL2ben.gifv
4) Shield -
Indication: Boss will shield itself.
What would happen: Didn't see a video that where they failed, so no clue, assuming a wipe.
What to do: Break the shield (dps the boss from its back), endurance debuffs should work (or priest's only).
Link: http://i.imgur.com/Fy6djb9.gifv
-boss attacks:
1) The spit -
Indication: Boss marks a target with an orange AOE circle.
What to do: iframe it, or block, both doable from what i saw.

2) Headbutt AOE attack -
Indication: Boss puts his 2 claws on the ground from both sides of his body, his next attack will be a headbutt AOE.
What to do: Block or dodge it, both available.
2nd Boss: Pirana
-special mechanics:
1) Poisoned Area -
Indication: Boss marks a target with a circle, and then throws a DOT poison on the target.
What would happen: Boss will throw a poison aoe in a few seconds (that sticks to the ground for a few seconds)
What to do: Could be iframed, but if not iframed, you have a poison debuff, and you need to run to the pool in the center of the arena, it will cleanse your debuff.
2) Adds -
Indication: Boss will have purple (purple/blueish) smoke coming out of him.
What would happen: Boss is going to summon adds.
What to do: Knock the boss down, stagger maybe works as well (didn't see a stagger in any video).
3) Crystal -
Indication: A text on the middle of the screen, boss will stop for 2 seconds and then start running to the middle of the map (cleansing pool).
What would happen: Don't know, easy to destroy, assuming a wipe.
What to do: Destroy the crystal, fast.
4) Pull to poison -
Indication: Boss nods his head 3 times in the same direction.
What would happen: Boss will pull everyone under his gut and then spill a poison aoe inside.
What to do: Grab can be iframed, poison aoe is cleansed in the middle of the arena pool just like in
special mechanic #1.
-boss attacks:
1) Drill -
Indication: Boss will turn around 3 times, before it lunges in one linear direction.
What to do: Dodge, or you will be hit.
2) 2nd Drill -
Indication: Boss bounces his head from the ground up, before it lunges in one linear direction.
What to do: Dodge, or you will be hit.
3) Waves -
Indication: Boss will create a circle of waves underneath him before he makes a duo wave (that damages).
What to do: First one you go closer to the boss, 2nd one you go further from it.
3rd Boss: Disc-dude
-special mechanics:
1) Lightning bombs -
Indication: There is none, its just going to happen from what I could tell.
What would happen: Boss will throw 3 "lightning bombs" with shockwave when they hit the ground.
What to do: Block or dodge first impact, when they are on the ground, destroy them fast.

2) Raging discs -
Indication: Boss will go to the nearest wall and emerge into it.
What would happen: Discs will start attacking on a linear (orange marked) direction from one wall to the other.
What to do: Go to a corner between the orange lines and don't get hit.
Link: http://i.imgur.com/VfA1pM9.gifv
3) Tornado -
Indication: Room will get dark (screen goes darkish blue).
What would happen: A wave of wind will emerge into all of the arena up until the circle in the middle.
What to do: Run to the circle in the middle, fast, its a safe-spot.
Link: http://i.imgur.com/6t9cKq0.gifv
4) OBA (On Boss Aoes) - there will be 4 shockwave aoe's targeted with orange circles, point is staying OUT of the orange overlay that fills the circle (or circles - between 2).
Indication:
What would happen:
What to do:
Link: http://i.imgur.com/7XfAeIn.gifv
5) Shield - *Possibly followed by OBA*
Indication: Boss will shield itself.
What would happen: Didn't see a video that where they failed, so no clue, assuming a wipe. BUT after the shield is broken, it might be followed by "OBA" (Special Mechanic #4).
What to do: Break the shield, then follow "OBA" instructions if it goes that way.
Link: http://i.imgur.com/VSYDa1o.gifv
-boss attacks:
1) Jump -
Indication: Boss will jump in the air, creating a shockwave aoe when he hits the ground.
What to do: dodge it, iframe it, block it, don't be close to the boss when it happens.
2) Disc Toss -
Indication: Boss will mark a random target (marked with a large orange circle) and then throws an AOE on it.
What to do: Dodge it by getting out of the way or iframing it if you're the target (or caught inside).

3) Bomb toss -
Indication: Boss will mark a target with a small orange circle, and then toss a bomb at it.
What to do: walk outside or iframe it.
4) Shockwave -
Indication: Boss marks 2 orange circles on the ground, and then throws a massive aoe for 2-3 seconds.
What to do: DO NOT stay in between those circles.

*GIFS ARE IN UPLOAD PROCESS*
Thank you, I was Abuse from [EN-PvE] Fraya.
Good luck on the Fate of Arun patch.