Night Elf Ancients

Many of the Night Elf buildings are actually sentient trees known as the Ancients. The Ancients possess the ability to draw their roots up from the ground and move around (albeit somewhat slowly). They can attack and defend, and there’s an upgrade available to them at later stages in the game that allows them to move more quickly. In addition to being mobile, the Ancients can also consume trees to heal themselves. The Tree of Life, the largest of the Ancients shown in the screenshot, collects gold for the Night Elves by rooting itself near a gold mine and then entangling it.
Also seen in this screenshot are Night Elf Wisps. These units expand themselves to form the Ancients and other Night Elf buildings. Wisps also harvest lumber, but they don’t mine gold.

Death Knight

Death Knights were once virtuous defenders of Humanity. However, they were corrupted by the subtle machinations of the Lich King and lured to his standard. These former heroes were given untold power and the promise of immortality in exchange for their loyalty. Although they retained their humanity, their twisted souls were bound to the Lich King's will for all time. Bestowed with black, vampiric Runeblades and shadowy steeds, Death Knights now serve as the Scourge's mightiest generals.

Abilities:

• Death Pack
  Can only be cast upon the player's units. The target will instantly die and a percentage of his remaining hit points will be converted into a magical shield that protects the Death Knight.
  
• Animate Dead
  Raises dead units in an area to fight for the Death Knight for a limited amount of time.