Heroic: Mana-Tombs

Quite a tricky achievement to solo as a Protection Paladin. The entire instance is about survivability, really, so you should probably wear your best avoidance gear.

The trash usually comes in packs of 3-5, where some will involve healers and Dark Casters. I'd recommend killing the Dark Casters first, as their mana burn can drop 50% of your mana if not resisted or interrupted, and the heals from the healers(Life-Binders, I think?) aren't really that great and has got a cast time of three seconds or more.

The first boss is quite easy, and you can even skip it at level 80 if you want, although that wouldn't be fun. Simply use your Shadow Resistance aura and nuke it with your back against a wall. When he casts the Dark Shell, just hold your damage for a bit.

After you've killed the first boss, you'll start encountering some Void Walker thingies. They have got abilities to silence, fear and reduce your spell damage, so just use Shadow Resistance aura for those and pull them back a bit to avoid getting feared into other groups. This is also where the healers and Dark Casters will spawn.

Once you reach the second boss, make sure to drink an invisibility potion, or something else that will allow you to slip by. He is close to impossible to solo, due to one of his abilities which stuns you and deals 50% of your maximum health as damage.

The trash after this will start hitting rather hard, but there'll be no more healers and only a few Dark Casters.

For the third boss himself, he's quite tricky. He will have three adds up once you engage him, which will turn into more powerful ones after a bit. The first adds only have about 6k health, and the ones they transform into will have 9k, so try to kill them immediately. I, however, usually weren't fast enough to kill them, so I had to kill a lot of the more powerful adds.

Meanwhile, the boss will be spamming Frostbolts at you, and occasionally throwing a Frost Nova or Blink away if you get too close. The frostbolts, along with the damage from the adds can turn out to be quite a lot of damage, so be sure to keep your Frost Resistance on. I even had to drink a mana potion I had got from the trash and used Lay on Hands as well.

Now, the thing about Shaffar is that his spells actually cost more mana than he gains, so if you manage to survive untill he's out of mana, the rest of the fight will be very, very easy. He'll continue spawning adds, but no longer cast Frostbolts on you. He'll still Blink every now and then, which keeps his mana at 0. Kill him off and get your achievement.

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Optional: If you're Exalted with the Consortium, you should be able to summon Yor as well. He's a horribly easy fight, and if you use Fire Resistance aura you can use Seal/Judgement of Wisdom without having to worry about your health.

Heroic: Mana-Tombs https://www.youtube.com/watch?v=vtEjt5L-2t4