The eternal hell of Mormonism-the second death, outer darkness, and the lake of fire and brimstone-will be the condition and place of ultimate exile for Satan, demons, and what the Mormons call the sons of perdition. Joseph Smith's vision description of eternal hell is found in Doctrine and Covenants 76:25-49.
The eternal residents of hell will consist of Satan (Lucifer) and the millions of demons who are the spirit-children that sided with Lucifer in the preexistence rebellion against Father God. Satan and demons were cast out of heaven without potential of receiving bodies and so were excluded from progressing into gods. Their final destiny in eternal hell has been sealed since their preexistence rebellion.
Permanently consigned to eternal hell along with Satan and demons will be the extremely wicked and rebellious who rejected the Mormon gospel in spirit-prison, and also the sons of perdition or Mormon apostates who once accepted the so-called restored Mormon gospel with full revelation, but later rejected it and fell away. This is how Dr. Robert Millet defines sons of perdition:
A son of perdition is one who commits the "unpardonable sin," the sin that will not be forgiven in this world or the world to come. One guilty of such an offense has enjoyed major revelation from God and yet has come out in open rebellion and opposition to the faith and thereby "sinned against the Holy Spirit." They inherit hereafter the kingdom of no glory.
Mormon apostates-those who turn away from the supposed LDS restored gospel and leave the Mormon Church-even if they join a Christian church and are faithful followers of Jesus Christ-will be condemned and will suffer in eternal darkness and torment of hell forever.
A Christian Perspective
Although there is a diversity of perspectives concerning the details of heaven and hell, the Christian position of Dr. Craig Blomberg is very persuasive:
The biblical texts that speak of the different experiences we will all have before God on the judgment day (such as 1 Cor. 3:10-15) never suggest that such differences are perpetuated for all eternity. On the other hand, the idea of degrees of punishment in hell does fit biblical teaching (Luke 12:47-48), and it makes sense logically. After all, the lost will be judged on the basis of works, not by grace, and unsaved people vary greatly in the amount of evil they perpetrate.