http://www.dcuguide.com/Who/MartianManhunter_Bio.htm
"The powers and abilities of the Martian Manhunter are a mystery to most people and to extent even his friends. He has the ability to totally control his physical structure allowing him to shape shift, morph fluidly, and even turn invisible or intangible briefly. Physically he is Superman's league in terms of strength and endurance, the only thing that can harm him is an intense fear of fire (inborn in all Martians it is the basis of the god H'ronmeer who as well as being the object of fear as a fire god is the god of death via association). The effect of the fear is to strip any Martian of their super abilities via the psychosomatic effect of their own body control working involuntary against them.
Martians also possess a range of undefined mental abilities, primary among these is the telekinetic ability to fly. They also seem to have a range of telepathic powers including mind reading and to an extent active telepathy. The extent and true limitations of these powers are not known. One of the most prised abilities of the Martians is the ability Mayavana, it is the gift to reach into another mind and create a mental reality as real as any normal reality. The strain of Mayavana is such that it can only be used once a life time and so is normally used on the one that a Martian loves the most, J'onn used it on the rampaging Despero so that he thought that he had destroyed the JLI (subsequently he reverted to a an embryonic state) and therefore save his friends."