Goblins

Weaker minions that become free do not always grow with killing. Some use the energy to make more of themselves - lots more. When this happens, the result is a goblin infestation. Individually, goblins are short-lived (they don't keep the energy they harvest), often lasting only a few weeks. The weaker the goblin is individually, the more 'children' it begets. A very weak sort of goblin may beget many children from a single kill, a very strong sort of goblin may require multiple kills to beget a single child.

As the initial goblin is a minion, like minions a goblin can look like anything - a shambling zombie, a little green man, a human skeleton, a red-skined winged lizard, little flying robots, pirates, ninjas, or anything else. One of the few things all goblins have in common is that they need to be dealt with swiftly, as a goblin tribe that finds enough 'food' (people) can very quickly become a massive horde capable of threatening entire nations.