Shadow Creatures

The void realm is a place of pure magic, inhabited by creatures so saturated in magic that they become part of it. The roving spirits of the shadows stay just there, and only on occasion may find their way out of the void realm. The less sentient a creature in the void is, the less chance it has to make it out.

Revenant
Revenants are the most common type of shadow creature. They are typically the remainder of a human sorcerer who has attempted, and failed, to harness the power of the void. Revenants are mindless, and have only one goal. They seek out and feed off of the most powerful magical creature near them, killing the host in the process. Revenants are immortal and cannot be damaged by conventional means; they must be sent back to the void, typically using arcane magic.

Shadow Mage
Shadow Mages refer to humans who have successfully tapped into the the power of the void, though this is rare. They can shift between reality and the shadows at will. Shadow mages still hold their mortal form, and can be damaged and killed. However, while in the void, they are immortal. Even a grievously wounded shadow mage can shift back to the void to rest and regenerate. It is only a matter of time before a Shadow Mage finds themself so infused by the void that they cannot leave, and sometime later become a Revenant himself.

Shadow Dragon
Typically dragons will not turn to the void for power. When they do try, they tend to be more successful than humans. Shadow Dragons, while still mortal while not in the void, are nearly impossible to kill, due to the increased resilience the power of the void grants them. Their longer life spans, and increased ability to control magic typically means they will not become revenants for some time.

Undead
The undead are arcane constructs. Though, forbidden and taboo, it is possible to tie the spirit of a revenant to the body of the deceased. These are capable of more complex individuality and thought than typical constructs. The experience and combat prowess that a revenant had while alive may transfer to the construct. Precious metals, such as copper, silver, and gold, interrupt the flow of arcane magic, and are therefore especially effective against the undead.