This is built from my comments in this post:
https://forums.elderscrollsonline.com/en/discussion/326414/so-here-i-am-thinking-about-my-build-daydreaming-theory-crafting-when-a-idea-just-came-to-my-mind
I can't say I have extensive knowledge on how skills work together, so I want to post this here and get feedback on how these weapon sets could be worthless,broken,improved,changed,etc.
Edit: These weapons would be additional loot drops from the final boss of a dungeon on Vet difficulty. Similar to how helmets are dropped.
Bloodspawns Teeth - Daggers (Spindleclutch II)
(1 piece bonus) Adds 250 Max health
(2 piece bonus) Flurry and its morphs heal for %5 of damage inflcted
Nerien'eths Disciple - Frost Staff (Crypt of Hearts II)
(1 piece bonus) Adds 250 Max Magika - %20 chance when dealing damage with Impulse or its morphs to summon a ghost spirit to fight for you for 15 seconds. It's basic attacks deal [x] amount of frost damage and snares the target
Leafseethers Sweep - Two Handed Axe (Elden Hollow I)
(1 piece bonus) Adds 1260 Physical resistance - Cleave or its morphs pulls enemies towards you when hit. 2 second cooldown
Hive Lords Rage - Mace and Shield (Darkshade Caverns II)
(1 piece bonus) Adds 250 Stamina
(2 peice bonus) While Shield Wall or its morphs are active, deal [x] damage per second in a 5m radius
Death's Charge - Sword and Shield (Vault of madness)
(1 piece bonus) Adds 250 Health
(2 piece bonus) Shield Charge or its morphs deal [x] more damage
Teethmashers Kneecappers - Maces (Direfrost Keep)
(1 piece bonus) Adds 250 Stamina
(2 piece bonus) Whirlwind or its morphs have a %20 chance to snare enemies hit
Leviathans Femur - Inferno Staff (Crypt of Hearts I)
(1 piece bonus) Adds 250 Stamina - When you roll dodge, create a wall of fire over the area you cover (probably something like a 10m long 1m wide AoE DoT), dealing [x] flame damage per second for 5 seconds (or just take the code from the morihaus set to deal flame damage when you roll through enemies).
Erthas' Summoning Circle - Bow (City of Ash)
(1 piece bonus) Adds 250 Magicka - When you deal damage with volley or its morphs you have a %10 chance to summon a Flame Atronauch for 15 seconds that deals [x] flame damage per attack and inflicts burning
Bloodbirthers frenzy - Swords (Fungal Grotto I)
(1 piece bonus) Adds 250 Health
(2 piece bonus) Each direct damage hit from Twin slashes or its morphs deals [x] shock damage
Lord Wardens Splintered Staff - Restoration Staff (Imperial City Prison)
(1 piece bonus) adds 1260 Spell resistance - Steadfast Ward or its morphs have a %10 chance to summon a ranged shade for 15 seconds when cast. the shades attacks deal [x] magic damage. This chance is increased to %100 when cast on an ally below 60% health.
Kinlords Spite - Two Handed Sword (Banished Cells II)
(1 piece bonus) Adds 4% healing taken- when you Critically hit with Uppercut or its morphs, spawn a Feast Orb nearby. Collecting this orb restores [x] health and [y] stamina. 10 second cooldown.
Ka-Nesh's Leeching Root - Restoration staff (Ruins of Mazzatun)
(1 piece bonus ) Adds 4% healing done - When you cast Panacea or it's morphs, summon a siphoning totem near you that drains [x] physical damage from enemies in a 5m radius, heals you for %20 of the damage delt.
Molag Kenas Force - Lightning Staff (White Gold Tower)
(1 piece bonus) Adds 64 Spell Damage - Elemental Storm or its morphs knocks enemies down for 2 seconds (this may be too OP)
Dark Siphon - Axe and shield (Elden Hollow II)
(1 piece bonus) increase health recovery by 60
(2 piece bonus) critically striking an enemy with a shield bash restores [x] magicka and [x] stamina, can only occur once every 10 seconds.
Atarus's Breath - Bow (Blackheart Haven)
(1 piece bonus) Increase weapon damage by 64 - Arrow Spray or its morphs deal an additional [x] poison damage
Uulgarg's Momentum - Two Handed Axe (Wayrest Sewers II)
(1 piece bonus) Cleave or its morphs are no longer a conal attack, instead decreasing the radius to 5m in a circle.
Foulhides Fangs - Swords (Selene's Web)
(1 piece bonus) Adds 250 Stamina
(2 piece bonus) enemies effected by the initial application of lacerate or its morphs are feared for 2 seconds. (or could workaround by casting a version of the NB fear initially)
Ganaktons Ward - Sword and Shield (Arx Corinium)
(1 piece bonus) Adds 1260 Spell Resistance
(2 piece bonus) Power Bash or its morphs deal [x] Shock damage in a 3m radius. 7 second cooldown
The Hive Lords Fist - Warhammer (Darkshade Caverns I)
(1 piece bonus) Adds 250 stamina - Reverse Slash or its morphs deal an additional %30 damage to nearby targets.
Angata's Staff - Inferno Staff (Banished Cells I)
(1 piece bonus) Adds 250 Magicka - When you deal damage with wall of elements or its morphs, you have a %10 chance to summon a clannfear for 15 seconds. The clannfears attacks deal [x] physical damage.
Allene's Daggers - Dagger (Wayrest Sewers I)
(1 piece bonus) Adds 250 Health
(2 piece bonus) when below 25% health, gain %100 chance to dodge the next attack. 10 second cooldown
Mephala's Hand - mace and shield (Fungal Grotto II)
(1 piece bonus) Adds 250 Stamina
(2 piece bonus) Light and heavy attacks have a %15 chance to summon a black widow spider, whose attacks deal [x] poison damage.
Whirlwind Charge - Two Handed Axe (Tempest Island)
(1 piece bonus) Adds 250 Magicka - Critical charge or its morphs now knock down enemies. No longer guaranteed Crit.
Butcher - Axes (Spindleclutch I)
(1 piece bonus) adds 250 Stamina
(2 piece bonus) With Blade cloak or its morphs active, killing an enemy restores [x] health
Gargoyles Gaze - Sword and Shield (Volenfell)
(1 piece bonus) adds %1 damage blocked
(2 piece bonus) Puncture or its morphs now petrify enemies for 10 seconds, dealing damage breaks petrification.
Frigid Touch - Frost Staff (Blessed Crucible)
(1 piece bonus) Adds 250 Magicka
(2 piece bonus) Critically striking an enemy with Destructive Touch or its morphs spawns a frigid banekin at your location. This banekin runs to an enemy and then explodes in a 4m radius, dealing [x] frost damage
For city of ash, can't think of a thematic way to link an ability with a boss.
Shadows Embrace - Daggers (Cradle of Shadows)
(1 piece bonus) 1260 Physical Penetration
(2 piece bonus) Hidden blade or its morphs deal an additional [x] damage when attacking from stealth.
I'd love to hear your ideas too