Instead of healing, the Dark Sage would shoot small bursts of rage and allow the troops it targets to have rage and increase there attack by small Burts like the healer does with healing.
200 Dark elixir for lvl 1
300 Dark elixir for lvl 2
400 Dark elixir for lvl 3
550 Dark elixir for lvl 4
Lvl 1 increase by 10%
Lvl 2 increase by 20%
Lvl 3 increase by 30%
Lvl 4 increase by 50%