Let's turn this back to being constructive:
What is damage mitigation?
To me, damage mitigation is simply a reduction in damage taken. Be it avoiding being hit, increased resist to take less damage, damage eaters, stuff along those lines. There is SOME merit to the idea that the quicker something dies, the less damage you take as well- but, I really don't consider that damage mitigation.
Things that mitigate damage:
DCI, Damage Eaters*, Hit Lower Attack, Armor Refinements (in either DCI or Increased Resist), Parry, Attunement (Spellweaving Spell), Discordance (Bardic Skill), Feint, Defense Mastery (Weapon Skill- allows you to break 70 resist cap), Tribulation (Bardic Mastery), Despair (Bardic Mastery), Perseverance (Bardic Mastery), Evasion (Bushido Spell), Mirror Image (Ninjitsu Spell), Hit Fatigue, Hit Curse, Curse (Magery Spell), Reactive Paralyze, Disarm (PvP mainly, it is usually not advisable to Disarm in PvM as creatures have been known to do more damage without a weapon equiped- Medusa--- I've never personally tested this and just going off what I've been told), Paralyzing Blow, Block (Special Move), Nerve Strike, Riding Swipe (vs Mounted Opponent), Bladeweave (Special Move- random), Force Arrow (Special Move), Force of Nature (Special Move), Infused Throw (Special Move). (that's most of them, I am sure I missed a few)
*Damage Eaters- are not really damage mitigation, you still take the damage, but are then healed. So, overall you do take less damage, since you are healed from the attack.
I had a discussion with someone who claimed that if you aren't being hit, that you are not mitigating the damage. My response was: You get attacked, you get hit, you take damage. I get attacked, opponent missed- who took less damage.
Combination of these effects increase how much damage you mitigate. Some are based on template, some are based off gear, others are based off what someone else is doing (Bardic Masteries).
Example- Mirror Images + Feint / Evasion + Hit Lower Attack + High Parry Skill + Perseverance + Armor Refinements to increase resist would mitigate a lot of damage.