Mormons are idolaters and go to hell when they die. Believing yourself to become a god is idolatry, as there is only one God.
Ezekiel 28:1,2 (KJV)
1 The word of the Lord came again unto me, saying,
2 Son of man, say unto the prince of Tyrus, Thus saith the Lord God; Because thine heart is lifted up, and thou hast said, I am a God, I sit in the seat of God, in the midst of the seas; yet thou art a man, and not God, though thou set thine heart as the heart of God:
Mormons believe that people on earth can be exalted to Godhood, whereas Christians believe that there is only one God.
Ezekiel 28:14-16 (KJV)
14 Thou art the anointed cherub that covereth; and I have set thee so: thou wast upon the holy mountain of God; thou hast walked up and down in the midst of the stones of fire.
15 Thou wast perfect in thy ways from the day that thou wast created, till iniquity was found in thee.
16 By the multitude of thy merchandise they have filled the midst of thee with violence, and thou hast sinned: therefore I will cast thee as profane out of the mountain of God: and I will destroy thee, O covering cherub, from the midst of the stones of fire.
God also spoke unto Isaiah regarding the fall of the person we know as the devil, from heaven and onto the earth.