Gear
For Trials and dummy parsing, Storm Master still comes out ahead but as much of the testing was done for overland or solo instances with this build, Noble Duelist would be the way to go.
With Oakensoul as a Mythic item that restricts other Mythics from being used and also restricting the usage of a second skill bar, we don't have too many options in terms of set availability and also makes us resort to a 1x bonus set such as Slimecraw's 1x Critical Chance bonus.
Jewelry enchantments can be primarily Weapon or Spell Damage glyphs as either glyph gives both Weapon and Spell Damage, however you will get an extra 30 additional Stamina Recovery with Weapon Damage glyphs for jewelry or 30 additional Magicka Recovery with Spell Damage (assuming gold).
Another alternative body setup can be 5x Order's Wrath.
Skills Review
The usage of Exhilarating Drain can be quite finicky as it's best to cancel out the full channel when you immediately get your Ultimate rather than letting the skill finish. However this is necessary as time is precious for DPS and going several Global Cooldowns without a Storm Atronach ultimate or Meteor ultimate can be a loss of damage.
While the Vampiric skill itself is a decent heal as well, if you need additional healing you can change the morph of Twilight Tormentor to Twilight Matriarch.
After testing with both morphs of Mist Form, the Elusive Mist form seems to be the better choice in terms of positioning and mobility. The healing from Blood Mist seems rather negligible and Critical Surge is infinitely better than it if you really want a passive heal.
We experimented with Simmering Frenzy and Blood for Blood and while in theory Simmering Frenzy could work with this build due to the amount of Health, it seems to trail behind Exhilarating Drain at least on a single target basis. Blood for Blood seemed underwhelming in terms of damage done.
Craft
Warfare
Fitness
Champion Points
Celerity is important to help you move out of danger as you channel heavy attacks. Bastion is a flex slottable, meaning you can slot something else you need if not casting a shield, such as Expert Evasion for a free Roll Dodge.
Instead of Backstabber, you can use Fighting Finesse should you not be able to flank enemies.
Introduction
This build can be used for a variety of content including overland (World Bosses), solo Arenas such as Veteran Maelstrom Arena & Vateshran Hollow, veteran dungeons and Veteran Trials.
Recommended race: Khajiit, Altmer (High Elf) or Dunmer (Dark Elf); for solo or 4-man content Khajiit will have an advantage.
Recommended food will be a bi-stat Health and Magicka food. For parsing or for fights where you don't need that extra health, you can use purely single-stat Max Magicka food! For soloing veteran dungeons, you may need to invest into a tri-stat food (Max Health, Max Stamina, Magicka)!
Recommended Mundus will be The Thief (for group content like Trials) or The Lover (for solo content and overland).
Potions can be your basic tri-stat restoration potions, however if you'd like to invest further into the build, you could go with Resistance Potions that restore 9206 Health immediately & gives Major Fortitude (30% Health Recovery), grants a unique 5280 Spell and Physical Resistances!
You should have about 25,000 resistances, making you basically a tank with around 30,000 Health (includes Minor Toughness if in group with a Warden).
The potion can be made using the following reagents: Mudcrab Chitin, Mountain Flower, Bugloss