Elder Gods and Defeat

The Elder Gods are different from the Gods of the Planes in many respects. They are older than the planes themselves and exist in the Far Realm, an alien place where the laws of the world are warped.
The Elder Gods cannot be imprisoned, killed or even injured by normal means. Instead great rituals with many individuals or specialized means specific to the Elder God must be used. For Example Maleash, the Imprisoned one was sealed within Alegxos the Eternal City by the Illithid Empire at the height of its power using the power of 5 Elder Brains to strip of Maleash of its power and bind it within the city permanently. It is believed that nothing will ever allow Maleash to fully leave its prison.
To Kill an Elder God, there must be something to take its place. They represent fundamentals of the multiverse and they cannot be destroyed, only changed to a new form. Ilkash, the Princess of Excess was once an unknowable entity before its being was absorbed by the mortal woman Ilkash. She was empowered by the being and reached the level of the Elder Gods, though it is not assumed this must be the case as some theories indicate that the being may be absorbed but the more power that is focused in one being the more likely it is that the new being will simply become much the same as the original. To be succeeded in this way an Elder God must be weakened and its form and power stripped down to a level close to the Gods of the Multiverse and only then can it be absorbed by the being or beings waiting for it.
It is not known why the Elder Gods do not prcatice this against each other but they seem to have an aversion to one another as their artifacts will repel one another and their cults avoid each other at all costs.