The Blackrose Prison Bow ("Virulent Shot" set) causes Scatter Shot to deal additional damage over time. However, unlike sets like Critical Charge Wild Impulse which add a separate DoT to an ability, Virulent Shot has a unique way of scaling:
2 items: Scatter Shot applies a damage over time effect that deals 65% of your initial attack as Poison Damage every 2 seconds for 4 seconds. The duration increases if you are farther away from your target to a maximum of 12 seconds.

To my knowledge, this means that Virulent Shot becomes the only effect in the game that "tripple dips" into the blue Champion points:

• Deadly Aim - Increase Single Target damage by 6%.
• Master-At-Arms - Increase Direct Damage dealt by 6%
• Thaumaturge - Increase Damage over Time by 6%.

The initial hit obviously benefits from Deadly Aim (Scatter Shot is single target), and Master-At-Arms. The DoT likewise benefits from Deadly Aim (again, you're applying the DoT to a single target) and obviously Thaumaturge (being a DoT), but will also gain 65%*6% = 3.9% bonus damage from Master-At-Arms, since it scales off the initial Direct Damage. Moreover, since the Direct Damage itself scaled with Deadly Aim, the DoT dips into Deadly Aim twice (once for scaling on initial Hit, once for being a single target DoT itself).

A Dragonknight using Obsidian Shield and the Naga Shaman set can buff themselves with Minor Vitality, Minor Mending, and Major Mending using a single, back-bar'able ability for a total of 43% extra self-healing.

Naga Shaman:
5 items: When you apply a damage shield to yourself or an ally, you gain Minor Mending and Minor Vitality for 6 seconds, increasing your healing done and healing received by 8%. This effect can occur once every 6 seconds.

Obsidian Shield: Grants a damage shield for you and nearby allies [...]. You also gain Major Mending, increasing your healing done by 16% for [...] seconds.

5 items: When you deal damage with an Execute ability you infect the enemy, dealing 948 Poison damage over 6 seconds and dealing up to 100% more damage to enemies under 100% Health. This effect can occur once every 6 seconds per target and scales off the higher of your Weapon or Spell Damage.

(948 is the *base* damage)
I bring this up because I've seen confusion in the past over what exactly constitutes an "Execute Ability" - the confusion probably stemming from the game having an actual ability called Executioner - a morph of two-handed Reverse Slash.
In reality, Execute Ability refers to any ability that specifically gains bonus damage against lower health enemies¹, and there aren't even restrictions on number of targets, or procs per cast (there used to be, but no more).

• Bow - Poison Injection (morph of Poison Arrow)
• Dual Wield - Whirling Blades (morph of Whirlwind)
• Twohanded - Reverse Slash (and its morphs)
• Nightblade - Assassin's Blade (and its morphs) ²
• Sorcerer - Mages Fury (and its morphs) ²
• Templar - Radiant Destruction (and its morphs)

Poison Injection, being a DoT, will reliably proc Sheer Venom 3 times or so per cast, and abilities with an area of effect (such as Whirling Blades) will proc the Sheer Venom DoT on *all* enemies hit.

¹ This does not take passive bonuses into account. E.g. The Dual-Wield Slaugther Passive doesn't make every Dual-Wield ability count as an Execute.
² Note that the enemy does not have to be below the 25% activation threshold for this to count as an Execute.

Baron Zaudrus's monster set has mostly seen usage as a hotter than a Deadlands jacuzzi pretty cool piece of fashion.
2 items: Applying a status effect to an enemy grants you a stack of Zaudrus's Ambition for 10 seconds, up to 3 stacks max. When you gain 3 stacks, the stacks are removed and you gain 4 Ultimate. On gaining Ultimate, you cannot gain additional stacks of Zaudrus's Ambition for 1 second.

The idea of generating ultimate with status effects is troubled by two conflicting trends:

1. To generate status effects you usually need to deal damage with different elemental types, and use weapon damage enchantments. I.e. you should be a Damage Dealer.
2. Damage Dealers have better Damage Dealing sets.

However, taking a look at the Elemental Susceptibility skill...

Elemental Susceptibility: Send the elements to sap an enemy's defenses and afflict them with Major Breach for 30 seconds, reducing their Physical and Spell Resistance by 5948. Every 7.5 seconds the enemy is afflicted with the Burning, Chilled, and Concussion status effect.

And the three Status Effects are applied instantly with every cast. Meaning...
By spamming a zero cost spell you can generate 4 Ultimate per second, which is more than Minor and Major Heroism combined!

Rush of Agony:
5 items: When you deal direct damage with a Blink, Charge, Leap, Teleport, or Pull ability, pull enemies within 10 meters to you. After 2 seconds, deal 1705 Physical Damage to all enemies within 7 meters. This effect can occur once every 8 seconds and scales off the higher of your Weapon or Spell Damage. The pull will not apply Crowd Control Immunity to a target.

Dark Convergence:
5 items: Casting abilities that leave an effect on the ground will create an area that applies a 60% snare and pulls enemies after a 1 second delay, stunning them for 1 second. After 4 seconds, the area deals 821 Magic Damage to all enemies in the 10 meter area, and 1642 Magic Damage to enemies within 3 meters of the center, increasing by 50% for each target. This effect can occur once every 25 seconds and scales off the higher of your Weapon or Spell Damage.

While these two sets are chiefly associated with PVP 'bombers' and 'ball groups' running over dozens of enemy players in a flurry of AoE damage, they actually fit surprisingly well into the builds of dungeon-clearing tanks.
Either set has a simple, dependable proc condition (that can be constrained to one bar) and help stack enemies up for expedient obliteration by your Damage Dealers.

Rush of Agony can be reliably proc'ed with Critical Charge (2-handed), Shield Charge (1h/shield), or any of the several class jumps and charge abilities.

While the game never had Taunt skills that could hit multiple targets at once, a certain item set actually offers a workaround:

Tormentor:
(2 items) Adds 1206 Maximum Health
(3 items) Adds 4% Healing Taken
(4 items) Adds 4% Healing Taken
(5 items) When you deal direct damage with a Charge, Leap, Teleport, or Pull ability, you gain 3642 Physical and Spell Resistance and taunt the enemy to attack you for 15 seconds.

Note the complete lack of cooldown on the (5)-piece bonus.
This means that, provided your Charge/Leap/Teleport ability does area damage, you can apply taunt to as many targets as can fit in the ability's AoE!

Some popular choices are Critical Charge (Stampede Morph) or the Templar's Explosive Charge ability.