This is a fight that follows a fairly stable formula throughout with only a few small quirks to mar the simplicity.
The fight swaps in and out between the Twilight realm and the regular realm, with the switching being handled by a context sensitive button in the middle of your screen called “Heroic Will” which will boot you out of the Twilight realm for a few seconds.
The main use of this is to deal with an ability called Hour of Twilight where the boss essentially kills everyone that remains in the Twilight Realm.
Due to the nature of the fight, you’ll have various buffs on you that will lower the cooldown of your Shield Wall and other class specific defensive abilities and also extend their duration so you generally never have to worry about having a cooldown active for this ability. When it comes, as three people NEED to remain behind to be hit by it or the group will wipe, more than likely, as a tank, you’ll be tasked with staying behind and surviving the blast with your cooldown.
Keep in mind that should you need to use that cooldown for any other reason and end up not having something ready when the Hour of Twilight is about to be cast, communicate with your raid so that they can make other arrangements ahead of time.
The other ability to keep an eye out for as a tank is one called Fading Light. Ultraxion will lay this down on a tank and two other raid members. When the duration of the debuff ends, if the character is in the Twilight Realm, they will be killed so when Fading Light Happens, there is usually a need for a tank swap as the affected tank returns to the normal realm for a brief interval and the secondary tank assumes the job of keeping the boss busy until it rotates out again.
For the tanking role, this is actually pretty much it.
Other aspects of the fight that’s good to know is his buff called Unstable Monstrosity. This buff causes him to do a pretty significant amount of shadow damage split among everyone that’s currently in the Twilight Realm.
He’ll cast this every few seconds but as the fight drags on longer and longer, he’ll begin to cast this more frequently so keep a closer eye on your health and your cooldowns as the fight drags on and be prepared to use a cooldown if things get hairy a little later on.
Finally, Ultraxion has a hard 6 minute enrage timer that will kill everyone in the raid if he isn’t killed so when you start coming up to that 5 minute mark of the fight, pop everything you have and do what you can to survive and help your raid finish him off as best as you can.