Additional information given credit in the original post guys.

The red text seemed to be every 10% of the mob's HP and his root seems to last a long time. If you have high enough DPS you can keep him rooted for most of the fight

The elemental damage is trivial, better to go full burn.

Red AE does need jousting. Swarm and standard pets can lock the named in place after the joust and don't seem to get killed by it. so if you tank him in the L shaped pool he'll more or less stay in one corner while the raid burns him from the other.

Adds spawn ONLY if your next to the eggs they hatch from and being in the water seems to counter their normal radius as well as the wingbeat style rear knockback that the name has.
At 10% and below Hoarfrost starts to teleport the raid into the center of the room, there are 4 or 5 egs in that area, best bet is to keep the name at the teleport point and ae off-tank the adds in the water. Kill the name then finish off aby adds still left alive. The adds are ^^^ heroics.

If the name ends up on the traid while about to red-ae simply run to the opposite corner where the tank usually sits.

grats on the new token and some easy loot.

Some of the adds during the fight are proximity based. IE if you get too close to a set of eggs when you joust, one add will spawn per egg.

At 10% the mob ports and summons people to the center of the room, causing all the eggs in the vicinity to hatch.

Nice addition. Should add a thumbnail to it. Have a clear screenshot of him?