The Blood Mage is the most hated character class in the story, but is also one of the most powerful. Once you have taken that specialization, you gain access to abilities that can enhance your spells and let you use your health instead of mana to cast them. If you can maintain your health and keep distance, you can become virtually unstoppable as you bring death wherever you go.
The objective is to create a mage that can survive both his enemies and his own abilities since Blood Magic can kill if used improperly. With the proper distribution of attributes, the right abilities, and the best items, you can make a formidable Blood Mage that can cast spells continuously and take out hordes of enemies without batting an eye.
For most mages, they may require a lot of Willpower in order to keep all their sustained spells up and still cast a substantial amount of damage and debuffs before needing to drink a mana potion. This isn’t really so for the blood mage as you do use HP with that specialization. In this case, you need only 31 Willpower for equipping items.
Most of the remaining points should go to Magic to maximize your offense, but you may want to stick it to 44 to use the best staff in the game, then put the rest in Constitution if you’re really going all out with the Blood Magic. From here, you will need nothing else and just focus on getting your abilities allocated properly and purchase the best items.
Grave Robber and Sacrifice are necessities as you can’t be healed by spells and potions with Blood Magic active. Getting their upgrades is also recommended to increase survivability. Hemorrhage is your main debuff spell that has AoE, and its upgrade turns it into crowd control as well with an AoE paralyze effect. Blood Slave is also fun to play with, letting you control a normal enemy that has blood and making him fight for you.
You should get everything that will do tons of damage. That means your second specialization should be Force Mage by default since that skill tree helps you draw gigantic numbers on multiple enemies during battle with its various crowd control spells. You can then take Primal Magic and whatever sustainable abilities that you can take. As you gain more spells, you can take more advantage of your deep health pool.
The reason why you may want to take Primal Magic over Elemental Magic in this case is because of its balance between offense and defense. While it has AoE spells that can blow cannon fodder away, it also has more focused crowd control spells like Petrify and a defense booster in Rock Armor. While Elemental Magic is very good in terms of damage and is no means an inferior skill tree, the Primal Magic tree is better for Blood Mages as survivability is an issue here. You can always have a companion take Elemental Magic anyway.
If you seem short in ability points, skip Blood Slave, Petrify, and the Kinetic Burst upgrade as they can be taken by another mage in your party. If you’re looking for party buffs, remember that other characters may get it for you so that you’re free to use ability points on something else. Some Entropic and Spirit spells may be useful as well. As for healing spells, you can use them if you turn off Blood Magic, so perhaps you can take those too.
It’s pretty challenging to play a Blood Mage in Dragon Age II, especially since Arcane Warrior is no longer available. Back in the first game, all you had to do is to combine the Blood Mage and Arcane Warrior specializations to create this sublime mix of magic and physical prowess that makes the most of your abilities. You don’t have that now, so you have to at least look for something to make the most of what you’re left with. Fortunately, there is a way to breeze through the earlier parts of the game with just one item.
In Lowtown, there’s a merchant that sells Neophyte Robes, which requires 16 Magic and Willpower to be worn. What it does is improve your Health to Mana ratio for Blood Magic by one point. This quality is also found in other items, so wear them whenever you can. Soon enough, you can have as high as a 4:1 health to mana ratio very early on, which greatly increases your effectiveness once you get the Blood Mage specialization.
Take note that if you switch to heavy armor, then you actually get nerfed to a support-oriented build. While you may have lots of health and strength, your magic damage is considerably weakened. But this is still a pretty good build if you take the Spirit Healer specialization. It has a lot of sustained spells that may use up a lot of your mana, but it will make your companions nigh invincible. You may hit enemies with various crowd control spells to make the fight much easier and cast healing spells on party members to keep them alive. It’s just that heavy armor won’t do much good here since you won’t have enough taunt capabilities to tank the enemies and make the most of the armor. You can be a support Blood Mage even without the armor.
A second mage is recommended to provide further support with party buffs and additional damage. You’ll also need a tank to take damage for you, so either Aveline or Fenris can fill that role. You may have either two tanks and a mage or a tank, a mage, and a striker. The striker must be able to deliver damage either from a distance or when unseen, so you can use Varric, Isabela, or Sebastian for that role.
While a Blood Mage is powerful, party members still need to be there to take the pressure off your character in order to not get killed. The key to invincibility in this case is to take every HP regen that you can find in order to both stay alive and never empty your pool for casting spells.