An immortal unit will attempt to return to its province of origin when it is killed. Depending on the unit there may be a delay of some number of turns, which is indicated in the ability description. A unit which reforms its body successfully may cure some of its afflictions in the process.
There are however a number of means to prevent immortality from triggering. Any form of mind hunt. Certain items such as the also provide this effect. Additionally, if unit's origin province is not under control of its owner when an immortal attempts to reform their body, they will be unable to come back and will function as if they had died a normal death., whether through the spell of the same name or another such as
Immortals may also be mitigated by using spells such asor which take ownership of the immortal rather than killing it.
A number of variations exist of standard immortality, which impose additional conditions.