I just posted a guide on how to obtain the Blood Knight's robe, a unique robe of the Blood Elf Paladin, and here's another guide on how to obtain the Illidari's robe. The Illidari jersey comes in two colors, green and purple. The appearance of purple is as shown below:
Green is as shown below:
Getting this robe is very simple. First go to Shadowmoon Valley in Outland, west of the Temple of the Stars:
There is a mountain road to the west of the Temple of the Stars, and the road is full of blood elves under Kael'thas:
This road will be patrolled by an elite [Vasarek the Conqueror] riding a chocobo, accompanied by four followers on horses:
You can make a macro [/tar Conqueror] to find him. This elite refreshes very quickly. It seems that it will refresh in less than five minutes after death.
After you kill him, you will find a diary and give you a task:
Go to the side and hand in the task:
The NPC who turns in the task is sealed in the crystal. After turning it in, you will be given the next task. The task will reward you with a ring and two shirts:
The task is very simple, just fight a few waves of spawning monsters here, and there will be a grimace on a big crystal next to it. It is Illidan, shouting to you:
This mission has a bit of a bug. If you don't enter the battle immediately after the mobs appear, they will disappear and the mission will fail. You can give up the mission and pick up the mission again. Just pick up the mobs as soon as possible after they appear.
First there will be a wave of mobs, then two big beholders, and then an elite paladin will be summoned. After defeating them all, go to Shattrath and submit a mission to get a ring and two shirts:
These two shirt transmogrifications can also be found in the shirt:
If you haven't got it, you can go get it. If you have the cracked Death Skull, you can get it in five minutes.