Mirror guard

It is just fluff, no actual rules.

How about something like Chosen with a predetermined roll of +1 Initiative to represent them following his every whim as quickly as humanly possible and always being ready to let their lord bask himself in his glorious reflection from their shields. These shields in turn could all be enchanted and thus give the unit a 2+ armour save in total.
I have no idea how much they should cost though.
Seems only prudent that the only character that can ever join this unit would be Sigvald.

Mirror Guard (25? points per model)

If you take Sigvald the Magnificent as a Lord choice, you can take up to 10 Chosen to be his Mirror Guard. The Mirror Guard Chosen have the same profile and rules as normal Chosen, with the following exceptions:

- the Mirror Guard counts as a Core unit.
- they already have the Mark of Slaanesh
- they are equipped with Chaos armour, hand weapons and Mirror Shields. No other equipment can be bought for them, other than a magic standard.
- Sigvald must be deployed as part of the Mirror Guard, although he can leave the unit after deployment. However, no other character can ever join the Mirror Guard.
- As long as Sigvald has joined the Mirror Guard, do not roll any dice, if a model of the Mirror Guard is required to roll on the Eye of the Gods table. Instead, it is always counted as having rolled the Dark Fury reward.

Mirror Shield.
Mundane shield. The Mirror Shield has been polished to such a degree that it acts as a mirror and, if conditions are right, can reflect the sun, blinding or confusing the enemy.

If an enemy missile unit using ballistic skill targets the Mirror Guard, roll a D6; on a roll of 4-6, the enemy shooting unit will suffer -1 to Hit.
If a spell that requires line of sight targets the Mirror Guard, roll a D6: on a roll of 4-6, the Mirror Guard gains a 6+ ward save against any wounds caused by that spell.
If the Mirror Guard is engaged in close combat, roll a D6 at the start of each close combat phase. On a roll of 4-6, enemy units engaged to the front suffer -1 to Hit in CC. As long as Sigvald is part of the Mirror Guard, on a roll of 1 Sigvald is so mesmerized by his own image in one of the Mirror Shields, that he cannot conduct any close combat attacks in that phase.