ALL THREE of these quests are done together while in possession of the shade.
The previous quest Parting Gifts familiarizes you on how to possess one of the shades using one of the red orbs found beside the questgiver. It's fairly simple as you click one of the red orbs, which will put you in the body of the shade controlling it.
This shade acts as a vehicle with the following controls.
The first thing to note is that your shade is stealthed...it's very easy to get by enemies or sneak up on them with the exception of the hounds you have to feed, they will detect you. You can also get caught in AOE on the stairs, but it won't aggro you, just annoying when you're going down. Also, you can easily be detected if you run through enemies, especially sleeping hounds. Just avoid getting too close to anything if you're unsure.
1 - BLINK : Teleports the Shade 15-20 yards forward.
2 - LIFETAP : Drains life from the target and gives it to the shade. You shouldn't really need to use this at all.
3 - PHASE : Shifts you from your stealth modes and increases movement speed. Use to get away from combat (use with BLINK).
4 - FEED HOUND : Throws food at the targeted area, used to feed the roaming hellhounds.
5 - ASSASSINATE : Used to depatch Restless Lookouts. YOU MUST BE BEHIND THE TARGET TO USE IT.
6 - BANISH CRYSTAL : This ability is used to banish nearby scourge crystals.
All quests take place in the same area. Take control of your shade, head southwest of the questgiver, go down the stairs and keep following the path, you'll see the hounds roaming around and lookouts on ledges, it's not far from the Shadow Vault.
An Undead's Best Friend
The quest asks you to feed hellhounds. This is simple and will be useful for getting around these dogs as they can easily detect you if you're nearby. Use your "feed pet" ability and throw the food in front of them. Once they eat it, they'll fall over and go to sleep. This only last for about 15-20 seconds, so eventually they'll pop back up and resume wandering. You can repeatedly feed the same hounds and they will count towards the quest.
Honor is For the Weak
The quest asks you to assassinate Restless Lookouts which you'll find perched on various edges. This is very simple, find a lookout, walk up behind him and use your "Assassinate" ability. You don't have to bother using your blink ability (unless you just want to speed things up) as they do not detect you. That's really it. If you do manage to aggro one, you won't be able to use your assassinate ability (as you'll be unable to get behind him), but you can kill him using your lifetap and it WILL count for quest credit. It's painfully slow though, so just walk up behind them, assassinate them and you'll kill them in two blows, virtually no fighting.
From Whence They Came
The quest asks you to banish scourge crystals which are large purple crystals floating on various pillars. They are easy to spot, just walk up to one and use your "banish scourge crystal" ability and it'll have you channel a beam into the crystal and destroy it after about 10 seconds or so of channeling. Simple.
AFTER YOU COMPLETE THESE QUESTS, YOU DO NOT HAVE TO TRAVEL BACK TO THE QUEST GIVER, SIMPLY LEAVE YOUR VEHICLE AND IT WILL RETURN YOU THERE
All in all, these are three fairly simple quests. The Restless Lookouts and Scourge Crystals have short respawn times, so you should be able to do all three quests within 5-10 minutes of time at tops. There are also skeletal workers that hang around, but I never aggroed them, so they shouldn't be of any concern.
After turning in these three quests, it will open up the following two quests. You will also be unable to take control of another shade after completion.
Seeds of Chaos
Amidst the Confusion
Good luck all and hope this comment is helpful.