He will be physically misshapen, and will be blind in his left eye. His right eye will be present but it will be dark (black). In a number of hadith he is referred to as one-eyed.
He will ride a white donkey which can cross seas, fly over land, and crawl under Earth.
He will deceive the faithful, teaching them that Heaven is Hell and vice versa.
The arabic letters "Kaa" "Faa" "Raa" (kafir, meaning "disbeliever") will appear on his forehead and will be read by all true Muslims regardless of them being literate or not.
He will be able to see and hear many things in many places.
He will have the power to work miracles in order to mislead believers.
He will try to put man on God's throne.
He will have what appears to be water and fire with him and call them Paradise and Hell: what will seem to be fire will be cold water (or Paradise) and what will seem to be water will be fire (or Hell).
He will claim to be God and will deceive people into thinking that he has risen the dead. One particular person he will kill and then say he will now resurrect him, whereupon Allah will resurrect him. He will not have this power again.
Those who reject and refuse to believe in him will suffer drought and famine whereas those who accept him will be living a life of plenty.
Some traditions of Islam relate that he will appear at Isfahan, and that he will rally the Isfahan Jews and many former Muslims and Christians to his support.
He won't be able to enter Mecca or Medina.