If you are here about Black Blood Residue, inside the instance, if you don't run straight to the boss, there are side quests in the instance, I personally didn't see anything on the side of my screen explaining these side quests. As I ran through exploring i would see something complete. A couple of side quests i remember off the top of my head was "Kill 3 gnomes" or something and another quest to plant 8/8 bombs, the bombs are highlighted in game and pretty big, as big as a gnome lol. There are some tougher mini bosses. I uploaded a screenshot to show the box the Black Blood Residue comes in. It is where you pick up your reward at the end of the instance, in another chest next to the one you get if you just go right to the boss. Have a great day!
Extra note: (@Lulubelle33) After you complete the side quests, there is a portal that opens up by the bank/auction house, in Stormwind, where the bulletin board is in town center, if the portal isn't there, then the side quests are not complete yet. once you take the portal to the Cathedral you will be in front of the Final Boss entrance!