Immortality

Immortality is something that can affect any sentient creature, and even some non-sentient, rendering them undying in one respect or another. There are three essential forms of the condition: essential, physical, and metaphysical.
With Essential Immortality, the subjects are unable to die naturally, but can be killed. In other words, they won't die of old age, and likely are immune or at least resistant to disease, but can still be killed. Dragons are examples of this, as their bodies will never give out on them. Once they reach maturity, they will remain until they are killed by another creature. Vampires are Essentially Immortal, as they cease to age once turned. It is also said that this is the state of Yarn and Vidad Kyenmanic; Yarn made himself immortal, and then passed that immortality to his son. Part of Essential Immortality is - generally - great magical power. In some cases, this is how it was acquired, and, in others, it is simply an aspect of how they chose to use their lengthened life. Regardless, this can make many Essentially Immortal creatures become perceived and mythologized as Physically Immortal ones.
The Physically Immortal could also be called the truly immortal; these are the creatures that literally cannot be killed. Irmensul, if real, is an example of this, as the tree cannot be cut down. By feeding on the waters of the Deep, the tree has become a font of magic power, and completely incapable of death. Mikoslav Denisevic is also Physically Immortal, as he will always come back to life, regardless of what is done to him; this is recounted in The Tale of the Sanguine Spring.
The Metaphysically Immortal are those creatures that will endure even after they are killed. This is all of the Progenitors, as well as Spirits. Being that they are made of born of raw elemental energy, they cannot be destroyed. Even if their bodies die, the energy that makes them up will reform into another creature, thus making their metaphysical self immortal.

Type

Physiological

Origin

Magical

Cycle

Chronic, Acquired & Congenital

Rarity

Extremely Rare