I'm putting together a stat block for Ebondeath and would like your input. Not the measly CR7 ghost presented in Divine Contention, but a real full powered ancient dracolich. Adding the dracolich template to an Ancient Black Dragon is... ok, but I want more. What would you add or change to the Ancient Black Dragon stat block with the dracolich template added?

For reference, the template adds; resist necrotic damage, poison immunity, condition immunities of charmed, frightened, paralyzed, & poisoned. and Magic Resistance.

That just seems uninspiring to me for a creature as legendary as Ebondeath.

What about some warlock class abilities like Mystic Arcanum (once per day spells of various levels)? What about Searing Vengeance, or Armor of Hexes? Maybe some invocations?

Or what about some of the demilich powers like; Antilife or Vile Curse? Or something new like...?