EditAppearance
They don't age particularly, except as a result of curses or similar kinds of harm, but they aren't immune to death. All other things being equal, they live until other events stop them.
They can be divided in many ways. For example, some Immortals are capable of learning almost any kind of spell, but with a limited ability to improvise spells on the fly. Others are bound to a particular element, but they can improvise their magic.
EditAnything Powers vs Elementalists
For example, Florian, the Lord of the Dancing Flame may learn and cast a spell that manipulates fire without spending any real time learning it. On the other hand, Judecca, the Lord of Rings would have to spend some time learning a fireball spell before he could cast it. He couldn't develop the spell in combat, for example.
Florian, however, couldn't ever learn a snowball spell. It is outside of the range of his element. The advantage that anything powers have is that they can learn to cast almost anything.Most of them have a hole, however, something that they can't do. For example,the Prince of Demons can't ever learn spells that annihilate. He can still learn spells that tear things apart, but he cannot deny something's existence.
EditQuestors
Some Immortals are Questors, and these are either anything powers or elementalists who serve some great universal principle. Masquerade, the Lord of the Masque, for example, would be a questor for 'beauty'. The Dark Hunt is a Questor who serves 'cruelty'.
These Immortals have access to a Miracle Pool. Miracle Pools are a reservoir of power that increases the efficiency of the Questor's normal abilities, casts spells on behalf of the Questor and, in extremis, alters reality.
The Miracle Pool has limited omniscience, and uses the Questor and his abilities as efficiently as possible. However, the Pool can only be triggered to further the aims of the Quest. And any points used (to cast a spell, for example) reduce the Pool by that amount.
Miracle points may be earned when the Questor successfully pursures their quest. It is important to note that the Questor earns no more power than a wizard or sorceror. If the Questor successfully pursues their quest, then all of the power they gained might be added to their Miracle Pool.
EditCosmic vs Astral
Some Immortals are cosmic in nature, and some are astral. Those that are cosmic draw their magic from the Abyss and beyond. Those that are astral draw their power from the Astral plane. Cosmic powers wane as they approach the core of a plane. Astral powers wane as they approach the Outer Darkness.
EditInitiation
As Immortals progress, they ascend to higher levels of 'initiation'. They may focus this progression in specific ways.
Example 1: They may improve their understanding of the properties of Feralie as it relates to their magic. This means that all of their spells become a little more efficient in that realm.
Example 2: They may reduce the casting costs of some or all of their spells, or to increase their effectiveness.
Whenever they reach a new level of initiation, they may advance a skill or proficiency that they know, and work on magical devices or instruments.