Using the idea from Dark Guardian VS Light Guardian, here is a suggestion of a new skill for Death Knight*.
*Maybe Paladin too, but then would be 2 roles with similar skills (Like Priest and Necromancer).k
Protective Spirit/Dark Guardian
Cooldown: 30/35/40/45
Summons the Guardian above the selected player for 15/20/25/30 seconds, dealing magic damage and taking 40/50/60/70% of the damage taken by the player (The Guardian cannot be attacked directly).
Depending on the weapon used, it's statistics change.
As the skill level increases, the Guardian's stats and lifetime increase.
Using Two-Handed-Weapons:
+ Damage
The Guardian appears above the character holding a big sword.
Using One-Handed-Weapons and shields:
+ Defense*
The Guardian appear above the character holding a sword and a shield*.
*Even if the Death Knight is holding only a sword (without the shield).