The Elves are a selectable faction at the start of the game if you have Return of the Elves installed (DLC). Elves have powerful but expensive units and are the best at maximizing research production. As living beings, they require food to grow cities.

They do have a much heavier reliance on Mana than other non-undead races (especially if you use their Temple units) but have difficulty mass producing it due to their inability to make Mana Vaults or more than one Mana Trap per city, so it may be wise to capture or build an Undead city or two devoted to Mana production.

Elves have access to the following special buildings:

Transmutation Facility (Built on Iron deposit), the Design Department (built on Neveril), and the Rectification Facility (built on Adamantium).