How about trials having a chance to have monster helm sets included.
Each of the trails could have one additional drop in form of a monster helmet.
The helmets can drop with a low change in normal mode (33%) but are a guaranteed drop in each vet mode run.
The shoulders have a chance to be included in the weekly caches of their respective trial!

Citadel of Hel Ra
Ra-Kotu's Wrath
(1) +Critical Weapon Chance
(2) Dealing Physical Damage has a 10% chance for creating a whirlwind of blades around the player dealing X physical damage to each enemy in proximity. Cooldown: 5 Seconds

Sanctum Ophidia
Ozara's Determinance
(1) +Magic Damage
(2) Dealing lightning damage to an enemy has a chance of 15% of calling down one lightning spear. The spear will deal X Lightning damage every half-second to all enemies in < 3 meters radius and hold the enemy on the ground (bosses are slowed instead of being hold).

Aetherian Archive
Varlariel Split-Personality
(1) +Life regeneration
(2) Being hit has a 10% chance of calling 1 illusion of yourself that takes over 20% of the damage you would've taken. If an illusion dies by its durations end, it heals yourself for its remaining life. Duration: 10 Seconds. Cooldown: 30 Seconds

Maw of Lokhaj
Rakkhats Visage
(1) +Critcal Magic Chance
(2) Dealing single-target damage to a target has a chance to shoot a barrage of 4 magic projectiles towards the enemy.
The barrage will empower itself. Each strike does 20% more damage than the previous one. Cooldown: 6 seconds