Lifeforce

Lifeforce is a life-giving energy, the Spark of Life that exsist within all living creatures. You can harvest it from creatures that has enough body mass to produce Lifeforce Orb, but creatures like Rats or Rabbits are too small to produce enough Lifeforce necessary to create a Minion. Lifeforce is needed to make new minions, and exists in four variants: Note that you can only harvest one sort of Lifeforce in Overlord: Dark Legend.
 * Brown Lifefore, which is found inside creatures of the Earth, like sheep or humans and it is the most common of all the types of Lifeforce.
 * Red Lifeforce, which is found inside creatures of Fire, like Magma Beetles
 * Green Lifeforce, which is found inside creatures of  Nature, and for some reason inside creatures that are poisious or stink, like Trolls or Puffer Beetles.
 * Blue Lifeforce, which is found inside creatures of Water and inside magic creatures like Boombos, Toads and Wisps.

Lifeforce appears in Overlord, Overlord: Raising Hell, Overlord II and Overlord: Dark Legend. In Overlord: Dark Legend only brown Lifeforce is found but it counts for all Minions.