Outside of clean execution, the only real source of damage on the fight is Fiery Ricochet, which the boss will cast every 18 seconds. It rebounds off players, and will create some burst damage. You can rotate your cooldowns aggressively as the boss will jump away for the intermission, giving you time to recover them.

The only real damage event is Break Water and is 1 hit of damage. Just make sure that people are topped before it hits and you should be fine!

This fight is challenging as there is a lot of movement involved, and the damage pattern is always very "brain-intensive".

Putrid Waters would be a standard double magic dispel mechanic (dispel one, heal the other while you wait for your dispel to come back) if you did not have to be careful of wiping your group because of the knockback on dispel. Setting up your UI to see your team nameplates could go a long way here to have a good idea of where they are. It is on a 20 seconds cooldown. This means that you do not have that much time to perform your dispels if you want it back up for the next wave. Again, very involved.

Slam is here to try and finish off the Putrid Waters victims. Be on the watch for its timer, and make sure to pop an external or a big ST heal on whoever is too low when it is coming up. I would recommend configuring your Boss Mod to have a countdown for it. This way you know exactly when it will hit, and it frees some mental space to focus on the debuffs. As you progress the fight, the successive tentacles will use it more and more (every 18 seconds, then every 13 seconds, then every 10 seconds)