Warcraft III: Reign of Chaos/Undead units

Death Knight
Supporting melee hero.
 * Primary skill: Strength
 * Abilities
 * Death Coil: Heals a target undead friendly unit or deals half as much damage to a living enemy unit. Cannot target mechanical units.
 * Death Pact: Sacrifices the targeted friendly unit, transferring a percentage of its hit points to the Death Knight.
 * Unholy Aura: (Passive) Nearby friendly units gain a movement rate and HP regeneration bonus.
 * Animate Dead: (Ultimate) Temporarily revives up to 6 non-mechanical dead units under the Death Knight's control, no matter their previous allegiance. If there are more than 6 corpses, it will revive the 6 strongest. In Frozen Throne, revived corpses are invulnerable and therefore cannot be dispelled (since invulnerable units are magic-immune as well).

Lich
Spellcaster hero with fast ranged attack. Abilities focus on dealing damage.
 * Primary skill: Intelligence
 * Abilities
 * Frost Nova: Strikes a unit with area-of-effect frost damage, damaging and slowing all nearby enemy units.
 * Frost Armor: Creates a shield of frost around a target friendly unit, increasing its armor. Enemy melee units that attack the shielded unit take frost damage, slowing their attack and movement speed. In Frozen Throne, can be set to autocast.
 * Dark Ritual: Sacrifices the targeted friendly unit, converting a percentage of its hit points into mana for the Lich. Highly useful in Frozen Throne as autocasting Frost Armor quickly depletes the Lich's mana pool.
 * Death And Decay: (Ultimate) Deals constant area-of-effect damage proportional to the maximum hit points of whatever is being damaged (e.g. 4% of the max HP of the unit/building instead of a fixed value; the stronger the target, the more damage it receives per second). Channeling ability. Also damages terrain overlay (i.e. trees).

Dread Lord
Tough melee hero. Abilities focus on disrupting the enemy.
 * Primary skill: Strength


 * Abilities
 * Sleep: Targeted unit falls asleep and is unable to move, attack or use abilities. Cannot be dispelled but instantly loses effect if the affected unit takes damage.
 * Carrion Swarm: Sends damaging wave down a linear path. Higher levels increase damage dealt by wave.
 * Vampiric Aura: (Passive) Nearby friendly melee units convert a percentage of their weapon damage into health with every attack.
 * Inferno: (Ultimate) Summons an Infernal at the targeted location. The Infernal spawns as a meteor, damaging and stunning enemy units where it lands. Infernals have high health and armor, Chaos-type damage (deals full damage to every armor type), magic immunity and a passive version of the Immolation skill that deals constant damage to nearby enemy units.