Just gonna say the stuff that isn't completely and utterly obvious (like adds):

First boss: After he bellyflops, he will either do expulsion (a point blank AOE underneath him that sends you flying) or an electricity attack where if you aren't in a small circle directly underneath him, you get hit and get a debuff. There's also bubbles that appear during the skill "Immersion" - they drop and create puddles that give you a debuff if you step in them. Don't step in them.

Morbol room after first boss: Every group has a chunk to take. Tanks pick up the moth & other thing on each side. Group burns them down while watching out for any "The Pagan's Knots" to kill or they'll explode and debuff the whole room, requiring standing on one of the platforms to "clear the air." After the moth & thing are dead, a morbol with spawn for each party. Once those are killed, you proceed.

Second boss: One tank takes Sawtooth and pulls him away from Irminsul (not even sure if this is a necessity?). After a certain point they'll both get a random debuff - one can't be attacked by ranged, and one can't be attacked by magic. If people get hit by brown goop, run through the lines connecting them to break them because otherwise those people can't move or use actions. When Sawtooth casts "Shockwave Stomp", line of sight behind Irminsul or you'll get one-shot.

Third boss: If she turns abruptly get the hell out from in front of her because she's gonna puke on you and kill you otherwise. Get out of the way of tentacles during "Flailing Tentacles" because they'll slam down. Get on platforms when the ground fills with bile. When Foobar adds spawn, kill them fast but make sure they absolutely do not get eaten by her "Beckon" AOE. After that, raid-wide damage depending on how many adds she ate.

Last boss: Turn away during Petrifaction. Stack in giant purple circle to split damage. When she splits into three adds, tank them as far as possible away from each other (there's almost always marks, but the basic point is that they can't be close to each other). The Echidna add also uses Petrifaction during this phase. Kill adds, raid-wide damage, rinse and repeat until she's dead.