Minis from 300 are mini-Immortals. They are feisty and violent, quick to attack even a PPC agent. They wear black robes and silver masks, and come equipped with a pair of tiny swords.
The Immortals were an elite group of soldiers in the Persian army during the Greco-Persian Wars, and specifically in this context, the Battle of Thermopylae. Compared to the original unit, the Immortals appearing in 300 are . . . a bit more fantastical.
The Immortals of this continuum are creepy and scarred-looking under their masks, with their teeth filed to points. Some fought using a primitive grenade-like weapon, which the Greek forces mistook for magic. They aren't actually immortal; the name comes from the tendency of the Persian army to immediately replace their dead members with new soldiers, giving the illusion of a fighting force with no end. The individual Immortals are quite killable, however, as the Spartans soon learned.