Powers and Stats
Tier: At least 5-C, likely far higher
Age: At least tens of thousands of years old
Classification: Demon Lord
Powers and Abilities: Warlock Magic
Attack Potency: At least Moon level, likely far higher (Far superior to Mongrethod, Dimensius, and other entities that destroyed entire planets, the latter over time. Lore states that the most powerful of Eredar can destroy planets, and Kil'jaeden is among the strongest. Magically superior to Archimonde who was going to destroy Draenor, see note)
Lifting Strength: Unknown
Striking Strength: Unknown
Standard Equipment: None notable
Intelligence: High (Manipulated the orcs into his service, is known as the deceiver which implies he's done similar things in the past)
Weaknesses: Nothing notable
Note: The Reason for the tiering, in the prophet's book, Velen, we see this quote.
"This last being leveled the rock sculptures around him, clearing a space where he could kneel in the dust made from his destruction and draw symbols of dread power with his clawed finger. When he finished, there was a moment of perfect quiet as the slaughter halted and the entire world waited in horrified stillness.
And then, an explosion.
The unleashed energies ripped the world's surface apart, and Anduin found himself crying out and throwing his arms up in terror, but the magics moved right through him without harm. The Legion marched back into the portal, returning to the dark nexus of the demons' dwelling, and in their wake was left... nothing." -Velen: Prophet's Lessions.
In this, a casual unnamed Eredar, effortlessly below Archimonde or Kil'jaeden, destroyed the crust of an entire planet.