Blood Infusion

Blood Infusion is the second part of the Shadowmourne questline. In order to do this quest you must be in 25 player mode(Normal or Heroic) and kill Blood Queen Lana'thel. To start the infusion, you must be part of the Blood Mirror for a second. This will apply a debuff which will do physical damage throughout the fight. You must be the second person bitten to do this quest so you can bite 3 people throughout the fight. The first bite will do 3k physical damage over time and reducing 10% damage. The second bite you cast will do 4.5k and reduce 20% damage done. The first and final bite will remove the debuff and apply "Blood Infusion" buff. You must not die with the buff and defeat Blood Queen in order to complete the quest.

Unholy Infusion

For this part of the Shadowmourne quest, you must be the abomination in the Professor Putricide encounter. In order to infuse Shadow's Edge you must be 1. having it equipped
2. Have 100 Energy 3. Estimating when to use the skill. As the skill cost 100 energy, that makes you'll be entirely wiped out on energy to unable to slow an ooze. Also the ability has a cast timer so you can't do it with any slime puddles up. After you use the ability, you will gain "Unholy Infusion" buff for 6 minutes. Death will remove this buff and you must kill Professor with the buff in order to get the quest finished.
Disc priests and Resto druids spec'd into revitalize will give energy back to the abomination. When you are using the skill, make sure the priest cast the bubble early for it to wear off in time and have your resto druid spam Rejuv and Wild Growth on you.
Using Unholy Infusion at 50% seems to be the best time.

Patch 3.3.3 This week!

As mmo-champion.com already pointed out, if everything is working correctly, patch 3.3.3 should be released this week. As the patch comes out. Unholy DKs will have another alternative spec to sub frost instead of sub blood. This allows more strength but the loss of Bladed armor makes indestructible potions useless. You will also hit 20% faster all the time. If frost fever is up, you'll hit 40%. Also for DK tanks. IT has it's threat generation increased.