My Stamina Dragonknight has finally been able to ditch all the fire damage in favour of almost purely Poison and Disease by replacing Draconic Power with Grave Lord. The only exception is the spammable, which remains Stone Giant, as the only Poison damage spammable is Venom Skull and I despise how clunky that skill is.

Item sets are Maarselok for head + shoulder, Poisonous Serpent dual wield weapons on frontbar + 3 body pieces, Azureblight and Asylum's Bow backbar (will be replaced with Master's Bow eventually).

Frontbar consists of: Venomous Claw, Stone Giant, Noxious Breath, Banner Bearer (DoT damage, Class Mastery + Berserk) & Detonating Siphon, with Flawless Dawnbreaker as ult for the Fighter's Guild passive
Backbar consists of: Poison Injection, Molten Armaments, Resolving Vigor, Banner Bearer & Grave Lord's Sacrifice, with Pestilent Colossus as ult.

It would be possible to go full Poison damage by swapping out Maarselok for Hand of Mephala and taking Animal Companions for Subterranean Assault instead of Detonating Siphon, but I like the visuals and theming of Maarselok and Azureblight too much to drop them, especially with Noxious Breath literally having an Azureblight-themed skill style already.

Another build I'm really loving is my Arcanist pirate, who dropped Soldier of Apocrypha in favour of Storm Calling. Tentacles and lightning bolts, fitting for a swashbuckler who was saved from a watery grave by a pact with Hermaeus Mora!

Item sets are Orpheon the Tactician for head + shoulder, Essence Thief 5pc, Vicious Serpent 4pc, Sea-Serpent's Coil Mythic (sometimes dropped in favour of Vicious Serpent 5th piece), and Maelstrom 2Hander backbar.

Frontbar consists of: Cephaliarch's Flail, Lightning Flood, Deadly Cloak, Travelling Knife (Physical Damage, Warrior's Opportunity, Major Savagery) & Endless Fury, with Flawless Dawnbreaker as ult
Backbar consists of: Hurricane, Recuperative Treatise, Evolving Runemend, Stampede & Fulminating Rune, with The Tide King's Gaze as ult

Lightning Flood procs Orpheon on cooldown, if it hasn't been triggered by something else (funnily enough, Essence Thief seems to count as "casting an ability that leaves an effect on the ground" and procs it), while the other sets could be changed to something else. I just really like Essence Thief and wanted to use it lol.

Those two are my properly and fully themed subclassing builds. Others that include a bit of theming are my Necromancer, who goes back to his roots as a Sorcerer by picking up Daedric Summoning in exchange for Living Death, truly making him the Daedra-worshipping necromancer that he is, as well as my Nightblade healer, who now has access to some necromancy of her own with Living Death. My Sorcerer Tank now also has damage shields galore with both Hardened Ward and Spiteward of the Lucid Mind, planning on also getting Brands of the Imperium or Foolkiller's Ward for him, so he can shield his allies as well.