Death Knight abilities use either runes (as part of the rune system) or runic power and are divided into the trees of Frost, Blood, and Unholy. As with the change to most classes in the Legion pre-patch systems Patch 7.0.3, several core abilities were either removed or moved to similar abilities from talent choices and many abilities were moved to specialization specific abilities.
Death Coil (Death Knight) (WC2, WC3, RPG, & Wrath) - kills target unit, damages a neighboring unit and/or heals the caster (WC2). Damage an enemy non-undead unit, or heal a friendly undead unit (WC3 and Wrath). Does damage to living and heals undead (RPG).
Death Pact (WC3, RPG, & Wrath)- Kill a friendly undead unit to restore the Death Knight's health (WC3).
Unholy Armor (WC2) - lowers target unit's HP and grants it temporary invincibility. Similar to Hysteria.
Raise Dead (WC2 & Wrath) - raises skeletons from corpses (WC2).
Haste (WC2) - temporarily increases movement speed of target
Whirlwind (WC2) -summons a whirlwind that moves around randomly to deal AoE damage
Unholy Aura (WC3 & RPG) - Increase the movement speed and health regeneration of nearby friendly units (passive).(WC3) a death knight may project an aura in a 10-foot radius that will heal damage to any undead controlled by the death knight and/or to those of evil alignment allied to the death knight, divided among those in the area of the aura’s effect as chosen by the death knight. The death knight can also heal himself. Those of good alignment take damage instead (RPG)... May be similar to Unholy Presence.
Animate Dead (WC3) - Raise up to six nearby dead units to fight for the Death Knight for forty seconds. Similar to Army of the Dead.
These are death knight abilities that are mentioned in the RPG:
Alabaster Skin (RPG) - the death knight’s skin hardens and grows pale, resembling marble or alabaster. (His hair also develops streaks of white, and some death knights’ hair goes completely white as they progress in power. The new skin is slightly tougher than previous flesh.
Contagion (RPG) - the death knight gains the ability to inflict disease upon a touched target. May have similar effect as Death and Decay but on a single target.
True Evil (RPG) - Death knights are immune to attempts to alter their alignment magically. Holy weapons and spells that specifically target those of evil alignment (such as holy smite), however, do 1.5 times their normal damage to death knights.
Undead Minions (RPG) - the death knight may summon the dead to fight alongside him in combat. Similar to Raise Dead and Army of the Dead, and the RPG's animate dead or create undead. It allows the death knight to cast either animated undead or create undead.
Crumbling Vessel (Hysteria) (RPG) - As he continues to embrace the darkness, the life force of the death knight ebbs as it is focused into strengthening and maintaining his physical form. His Constitution modifier is now added as a profane bonus to his Armor Class.
Life Stealing (Vendetta/Butchery) (RPG) - a death knight discovers how to leech the life force of those he slays in combat. For each living creature he kills, the death knight recovers energy.
Greater Death Coil (RPG) - Greater Death Coil does more damage than regular Death Coil & heals undead for more health.
Undying (RPG) - the death knight becomes immune to all death spells and magical death effects. This immunity does not protect the death knight from other sorts of attacks such as hit point loss, poison, petrification or other effects even if they might be lethal.