One year, 10 months and sixteen days and one expansion ago I spoke of obtaining the quest Unholy Infusion in my post Long Road to Shadowmourne... (Part 3).
The quest was simple. Use the Abomination Potion while fighting Professor Putricide in 25 man mode then save up 100 energy to use the Infuse Shadow's Edge ability. Also have Shadow's Edge equipped at the same time.
I was in a guild group getting guild achievements in the instance. I was with Hunterfaith, Xynzelle, Voros, Evea, Jezael, and Yig, I wanted to do my quest but we were also after Nausea, Heartburn, Indigestion... (25 player). Which meant while I was the Abomination I couldn't use the Regurgitated Ooze ability. We have Mists of Pandaria DPS now and this wasn't a problem.
I handed in Unholy Infusion. My next quest was Blood Infusion.
Blood Infusion is the quest where you have to become a vampire and bite three people during the Queen Lana'thel fight while having Shadow's Edge equipped. Something we couldn't do during this run. The problem everyone you bite will turn into a vampire. If they don't bite someone they will be mind controlled. So for me to bite 3 people, even if I was the first bitten, would mean we would need twelve people at least.
20 days later was in a group with Azadelta, Lushen, Owl (Exray). The four of us were able to get it done on 25 man heroic. I make sure to have Shadow's Edge equipped before we start.
Stage One: I rush in towards Queen Lana'thel with Owl while Aza and Lushen stand back. I get Blood Mirror. However Lushen is bitten, not me. Aza runs in and gets blood mirror and I stand near Lushen.
Stage Two: Sixty Seconds in, Lushen turns into a vampire and bites me. I need to wait sixty seconds to bite my first person for the quest. Lushen uses Ra'sha's Sacrificial Dagger so he dies and doesn't bite anyone else (if you don't bite someone every 60 seconds you will get mind controlled). We are down to myself and two others and I need to bite three.
Stage Three: After Sixty Seconds I can bite my first person. I bite Azadelta. Aza uses his own Ra'sha's Sacrificial Dagger so he isn't turned into a vampire like Lushen. Aza then uses a soulstone to get back up without the rebuff and at no risk of being mind controlled.
Stage Four: Another 60 seconds pass and I bite my second person. Aza again. This time Lushen uses Rebirth on Aza to get Aza back up again.
Stage Five: 60 seconds later I bite Aza for the third and final time. We then nuke the boss Queen Lana'thel before either Aza or myself have to bite anyone else. Quest Complete.
The next quest is Frost Infusion. I need Sindragosa to frost breath me four times. In my holy gear and Shadow's Edge, I cast Righteous Fury to tank the dragon. I am able to keep threat and after an Air Phase, I take the fourth frost breaths. After some damage the undead dragon is slain.
Next up is The Splintered Throne.
I will have to farm bosses in 25-man for 50 Shadowfrost Shard. This will take a few trips.