The Build

Torment:
This is rank 2 only to get to the other abilities. We do use it every 5s (if rng doesn't reset it) to apply another 15% mitigation on ourselves thanks to the "Shackles of Agony" rubies.

Rift of Pain:
This is what we use to make some aoe aggro, restore lots of Obsession at once and to pump our Wall of Blades, decreasing incoming damage by 5% per stack, a maximum of 5 stacks.

Torturer's Blades:
We use this ability very often. It helps us build Wall of Blades to reduce the damage we take by 5% per stack, up to 5 stacks. And also thanks to the "Eternal Night" rubies, we can extend our Dark Veil to unlimited time aslong as we can keep hitting mobs.

Ataxy:
We use this ability to apply the Vulnerability on mobs we're tanking, thus increasing the damage dealt by our group.

Shadow Flight:
A great escape tool! Instantly turns you into Fury form while also teleporting you away, with travel time all the less

But great for kiting in MOS, and getting around really quick.

Aspect of Defense:
Without this, we cannot tank

Lot's of rubies wouldn't work, we'd have half the health we need, we'd have less aggro

Sphere of Negation:
This is a nice back up defensive, but I have used it very rarely.
I'd save it when you panic, press the button and hope for you healer to grab you out of trouble

Stream of Chaos:
This is a great ability to apply aoe Vulnerability. Can be nicely timed after stunning by Demonic Onslaught.
Used to work on red rings only to slowdown, but that's been removed

Still a really helpful ability!

Veil of Madness:
Another great defensive ability we use often, or nearly off cd.
Also changed since the 11.1 update.
Now it reduces all incoming damage by 60% for 8s, with a cooldown of 16s. Before it used to apply a 300% shield on yourself at the cost of 30% health.
It's better than it used to be, because mitigations is what you need to survive bigger hits.

Expurgation:
We use this to heal up quickly during downtimes in combat, when all of them are cc'd for example incase you run without healer or healer's busy doing other healings.
It's takes a while to practice to swap quickly between forms and back to tank cause you cannot use this on tank form. Need to be on human form in order for you to use this ability.

Reincarnation:
Another great tool to aid our healers, and thus our own. It's a huge self heal that usually gets me from 30% to max. Survivability affects this one!

Ill Will:
We use this ability to help our healers because we're literal meatshields with lots of point to heal.
using this ability, thanks to the rubies "Will of Chaos", will increase all incoming healing by 60% - which is a ton really.

Demonic Onslaught:
This is our main Crowd Control ability. A great AOE CC ability with a very long duration, and really small downtime.
Stuns for 7s, cooldown is 10s

thanks to the "Thunder Onslaught" rubies. Have people throw aoidos fires inbetween and you have literal permanent crowd controls going on!
It's best to press the ability once and let it run out while making turns with our mouse.

Dark Veil:
This is one of our main defensive abilities.
It's also been changed since 11.1.
We can extend the duration of this ability by spamming Torturer's Blades. It also applies Weakness on all mobs inside of it.
It used to, instead of applying Weakness, give 40% mitigation to all party members that are inside the circle.

Temptation:
Another really good Crowd Control, but can only be done in Predator Form, so be really careful on when to use it.
Usually using this when a mob is chasing someone on which I lost aggro.

Sigil of Decay:
We use this ability to apply Vulnerability to our mobs. Small delay on it happening because the bomb on the floor needs to charge up for 1 second.
It's not an aoe, so be careful when dropping it in groups of mobs.