All melee attacks deal [0.48 * mw] to [0.48 * MW] additional Holy damage, but the Paladin loses health equal to 10% of the total damage inflicted. Lasts 30 min.
Unleashing this Seal's energy will judge an enemy, instantly causing [0.26 * mw + 0.11 * AP + 0.18 * SPH] to [0.26 * MW + 0.11 * AP + 0.18 * SPH] Holy damage at the cost of health equal to 33% of the damage caused.
Seal of Blood is the Horde's equivalent to Seal of the Martyr, allowing the Paladin to deal a large amount of Holy damage with every hit. However, in PvP, the backfire damage can be dangerous sometimes.
In numerous calculations from a retribution perspective, Seal of Blood has been proven to do significantly more damage than Seal of Command or Seal of Vengeance. The difference between Seal of Command and Seal of Blood is usually a margin of more than 15%.
This is NOT a good tanking seal. The main reason is that it depends on the damage-per-strike of the wielded weapon to be effective, which begs for the use of a 2-handed weapon, but tankadins need to wield a 1-handed weapon and a shield in order to be tough and effective. If a paladin stacks enough strength and attack power for the seal's damage to be effective even with a 1-handed weapon, his survivability will suffer. Synergy effect with Spiritual Attunement is not a valid reason to use this seal, as there are many proper ways to handle mana deficit situations for tankadins.
The Seal is based on the melee mechanics for hit and crit.
The seal only scales with weapon damage, not spell damage. It therefore heavily favors melee-geared Paladins (mostly Retribution Paladins), rather than spelldamage-geared Paladins. Note that the Judgement does scale with spell damage.
This seal is counted as a second melee strike in terms of game mechanics, meaning that the damage it deals can miss, be dodged, be blocked, and be parried. Since it deals non-physical damage, it can also be partially resisted when used against mobs that are higher level than the player. It will NOT activate Judgement of Light and Judgement of Wisdom nor any other weapon proc (fiery, mongoose, life steal procs, etc.).
When using a fast 2-hander, this seal deals more DPS than Seal of Command. Also, the fact that it can crit makes it shine in a raid situation since Vengeance is similar to a fury warrior's Flurry in terms of how it increases the paladin's DPS.
Seal of Blood's damage inflicted to the user is not capable of causing a Reckoning proc.
The Paladin Retribution talents Sanctified Seals, Vengeance, and Crusade all affect the damage dealt by this seal (prior to patch 2.1.2 there was a bug that would cause it to doubly affect the returned damage component of this seal, making the returned damage more than the 10% stated on this seal's tooltip).
In parses, the % crit may sometimes seem off. This is normally because of the backlash (self-damage), which cannot crit. Generally, in these cases you can double the posted crit rate to determine the actual crit rate.