This post doesnt cover every single thing related to aggro, but it should be a good guideline of the most common stuff.
Melee Damage
Auto attacks generate 1 threat per point of damage, plus a small amount of additional threat that scales with weapon delay and character level. Warriors get bonuses to this additional threat with the advanced anatomy AA. Level 65 warriors generate additional bonus threat when they riposte a target. Attacks that miss do not generate threat.
Hate generated by archery/throwing damage is reduced by 50%.
Spell Damage
Generates 2/3rds of the damage dealt as hate (single target nuke for 100 damage, generate 67 hate). Damage from Rains, PBAEs, and Targeted AEs generate 1/3rd the threat of single target spells (PBAE nuke for 100 damage, generate 23 hate).
DoT spells generate 1/4th of the damage dealt as hate. Shadowknights generate 60% of the damage dealt as threat, scaling up to 100% of damage dealt as threat with rank 4 Vexation of Blights (10%/rank).
Crits
Crits (both melee and spell) do not generate additional threat. If you crit for 200, you generate threat as if you did 100 damage. Applies to all damage AND all healing.
Damage Shield
Does NOT generate threat.
Healing
Generates aggro based on 1/3rd of the effective healing done (overhealing generates no threat). Paladins are the exception, and generate aggro based on 1/2 of the effective healing done. Group, raid, and ground-targeted healing spells generate hate at 1/3rd the rate of single target heals. Single target heal for 100, generate 33 threat. Group heal 1 person for 100, generate 11 threat. Group heal 5 people for 100, generate 55 threat etc.
Paladins generate 2 (two) threat from group/raid/ground targeted healing, regardless of the amount healed.
Enemy AI (Redtext aggro)
- Changes and full explanation of when enemy mobs notice and aggro players who are casting.
- An enemy who has been damaged with melee damage will not trigger this event.
- An enemy in melee range of top of hate will not trigger this event.
- An enemy rooted, snared, feared, mezzed, or unintelligent (hidden stat) will not trigger this event.
- An enemy that does not have a natural spawn point will not trigger this event. example: scripted spawns.
- Longer cast time spells increase the range in which an enemy will notice to trigger this event.
- Having lower health increases the chance this event will trigger.
- The more non-damage threat the primary target (the tank) has generated, the lower the chance this event will trigger.
- This event can only occur one time.
- A message will be displayed when the event occurs.
"%s redirects their attention to %s's casting." - The aggro lockout has been removed.
- When the event triggers, the enemy will have a guaranteed taunt effect applied to them by the caster.
- Longer cast time spells add more bonus threat to this taunt effect.
This mechanic does not trigger if you are not in line of sight of the enemies or sufficiently far away from them.
Bash
- Warriors, Shadowknights, and Paladins generate bonus threat with bash. This bonus is equal to player level plus shield AC.
- Shadowknight and Paladins get an additional bonus equal to shield AC times three.
Low HP Aggro
Your threat towards an enemy is increased by 5x while you are below 25% life and within 75 yards of the enemy.
Melee Range
- You have a 1.25x multiplier to your hate while you are in melee range of a mob. This is why mobs will turn to hit others if a tank goes to reposition a mob w/o a sufficient threat lead. Example: Tevp has 110 hate, Meow has 100 hate. Because they are both in melee this is boosted to 137 and 125 hate respectively. Tevp backs away from the mob and leaves melee range. Tevp’s hate is lowered back down to 110. Meow is now the highest on the hatelist, so the mob turns and attacks her, rather than chasing / summoning Tevp.
- This is a 2x multiplier for snared or permarooted enemies.
Runes
Generate half of the runes value in threat. Groupwide or raidwide runes generate 33% of the threat that a single target rune would.