Necromancer Tank Build
Necromancer tank builds make some of the best in The Elder Scrolls Online, capable of soaking up tremendous amounts of damage and sustaining themselves endlessly to take the pressure off healers. The valuable debuffs and group utility they offer are second to none, and a Necromancer tank is always a great addition to any team in ESO.
Gear Sets
Archdruid Devyric: This is easily one of the best tanking sets in The Elder Scrolls Online. With a simple heavy attack, you can apply Major Vulnerability in a wide area for seven seconds after a brief delay, which can be used to fill in the gaps between Glacial Colossus uses and keep that powerful Major Vulnerability debuff up a lot. Get this set from Earthen Root Enclave.
Saxhleel Champion: Since Necromancers have such excellent access to ultimate regeneration, and you will be wanting to use Glacial Colossus for greater uptime on Major Vulnerability, Saxhleel Champion works perfectly. By using this, you don't need to use Aggressive Horn to pass the Major Force buff to your group, making room for Glacial Colossus. You can find this in Rockgrove.
War Machine: Another ultimate-oriented set that will allow you to pass on the Major Slayer buff to your team members when you use an ultimate, boosting their damage output by a massive margine, especially when combined with Major Force and Major Vulnerability. This can be found in the Halls of Fabrication.
Puncturing Remedy: An important addition that allows you to heal yourself and boost resistances, all just by using your taunt. You can get this from Dragonstar Arena.
Skills
Pierce Armor: This is your primary melee taunt that is easy to keep up, and allows you to debuff the target with both Major Breach and Minor Breach, increasing your group's DPS.
Hungry Scythe: A melee spam heal that deals damage in a cone area and heals you. This is perfect since it costs Magicka and takes a lot of pressure off the healer.
Necrotic Potency: Since this build's gear sets work best with high ultimate regeneration, you can use this to siphon ultimate from nearby corpses, including the ones your Beckoning Armor and Spirit Guardian leave.
Agony Totem: An AoE stun that takes pressure off you and your group while keeping enemies in place.
Silver Leash: This is your main "pull", which allows you to grab distant minor enemies and pull them to you to make DPS easier.
Glacial Colossus: Your main ultimate - between this and Archdruid Devyric, you will be able to get excellent uptime on Major Vulnerability.
Destructive Clench: A ranged taunt that has the benefit of costing Magicka while also applying Major Main and immobilizing the target.
Elemental Blockade: This is a great support skill that has the potential to slow and root enemies in a large area, apply Chilled and Brittle to them, and provides a projectile shield to you and allies.
Unnerving Boneyard: This is a flex skill that is used to apply Major Breach in an area. You can switch this to more utility if it isn't needed.
Spirit Guardian: A heal over time that also increases your damage mitigation by a hefty 10% while providing corpses for you to use. Keep this up at all times.
Beckoning Armor: This is your source of Major Resolve that also pulls in ranged attackers, meaning you don't have to waste as much of your resources on Silver Leash.
Reviving Barrier: An amazing backup ultimate ability that can save your whole group in a tough situation, or protect them through certain mechanics.
Champion Points
Ironclad: This grants you a nice boost to your damage mitigation against direct damage attacks, which is one of the most common that you will encounter in PvE.
Enduring Resolve: Damage over time mitigation is very useful, since it counts for single target DoTs and area DoTs. This means that, in many cases, this will stack with Unassailable.
Duellist's Rebuff: Often stacking with Ironclad to further boost your resistance against single target attacks, this is a useful one for tanks in particular, helping to mitigate the heavy damage coming from bosses.
Unassailable: Helping you to stand in stupid for longer, Unassailable will reduce your damage taken from area attacks, helping towards taking the pressure off the healer.
Boundless Vitality: Every bit of health makes a difference, especially in some of the tougher content that The Elder Scrolls Online has to offer. This will help you bump yours up a little more, increasing your survivability.
Fortified: Similar to Boundless Vitality, one can never have enough resistances, and this will add a little extra to boost your survivability so that you can focus more on the task at hand.
Sustained by Suffering: Gaining the ability to regenerate resources faster when you have negative effects on you is just perfect for a tank, making this a smart choice.
Bracing Anchor: As a tank, you don't need to move that much, but you certainly need to block as much as possible, making this a great addition to your toolkit.
Mundus Stone
The Atronach is best suited for tank builds, boosting Magicka Recovery substantially, which is important for keeping up with buffs and subsidiary healing. Stamina can be regained through potions, heavy attacking and group synergy activation.
Food Buff
Tanks benefit especially well from Orzorga's Smoked Bear Haunch, boosting all recoveries along with Max Health as well. However, it is expensive, so if you need a cost-effect option, use the Bewitched Sugar Skulls, which are also very effective.
Race
The best race to use for this build is a Nord for its higher resistances and ultimate regeneration, but Argonians, Imperials and Bretons are also excellent options for their superior survivability and sustain.
Potion
Tri-restoration potions are generally the best for any tank to run, allowing you to manage your resources perfectly. However, when you are dealing with trash mobs and the like, you won't want to waste them, so carry some trash potions around for the parts that aren't very intense.
Mortality
The Undeath passive can be tempting for tanks, but running a Vampire on all but highly specialised and rather inefficient builds is a bad idea. The amount of fire damage found in PvE content, and the high increase to standard skill costs, will make running Vampire on a PvE tank a liability.
Notes
Necromancer tanks are my favourite, and with good reason. They present as more of an "advanced" tank class, but are easy to understand with a little bit of practise. The main thing to remember is that your job, in addition to taking all the pain and shrugging it off with ease, is to harvest as much ultimate as possible. Do this, and you will be able to use Glacial Colossus more often, activating your gear sets and delivering very powerful buffs to your group and debuffs to your opponents.
Any corpses in the area should be harvested with Necrotic Potency, increasing your ultimate by a huge amount per corpse. Spirit Guardian and Beckoning/Summoner's Armor will provide corpses when their duration runs out which can also be used to harvest ultimate, and you can even slot Blastbones to farm as much of it as you like if you wish.