Here's a list of what Hank/J'onn can do if he chooses (Source:
Wikipedia):
The Martian Manhunter possesses a wide variety of superhuman powers, including superhuman strength, durability, flight, regeneration, self-sustenance, shape-shifting, intangibility, invisibility, telepathy, telekinesis, extrasensory input, and optic blasts.
Many of his powers resemble those of Superman, including superhuman strength, flight, invulnerability, and "Martian Vision" (a term designating both the ability to see through solid objects and the ability to project beams of energy from his eyes). Superman once said of him: "He is the most powerful being on the face of the Earth".
J'onn uses his power of shapeshifting for various effects, such as adopting human or monstrous appearance, elongating his limbs, growing to immense size, altering the chemical composition of his body, etc. His default form during JLA meetings and in public is a "human-friendly" version of his actual birth shape.
J'onn can also phase-shift, becoming intangible to pass harmlessly through solid objects, or to phase through people and machines in order to damage them or cause pain. He can also render himself invisible, and he originally acted as an invisible hero or unknown "angel", helping those in need without revealing himself. In the Silver Age story "The Unmasking of J'onn J'onzz" he lost the ability to use his other powers while invisible and was revealed to the world as a Martian superhero, although his civilian identity of John Jones remained a secret.
A powerful telepath, J'onn can both perceive others' thoughts and project his own thoughts. He often acts as a "switchboard" between the minds of his teammates in order to coordinate their actions. The extent of his telepathic abilities is great; several times he has connected his mind to the entire population of Earth, such as in the Trial by Fire story arc,[55] in which he connects to the whole population of Earth in order to find a rogue telepath who has been brainwashing prominent criminals and political figures. He also uses his telepathy for creating illusions, locating other sentient beings, controlling other’s minds, manipulating memory, inducing sleep, travelling on the astral plane, transferring information to people directly, and creating brain blasts and mental shields.
J'onn can absorb energy beams and waves. His telekinesis allows him to move objects with his mind, which he describes as "Martian mind-over-matter". He uses his telekinesis to manipulate and move or push multiple objects, as well as to fly at high speeds and to create a telekinetic push or a telekinetic shield. The inner valves and chambers in his air canals are very dense and greatly enhanced, allowing him to create strong hurricane force winds just by exhaling.
J'onn's eyes can project energy beams, known as "Martian Beams", the exact effects of which have varied in different decades from incendiary effects to concussive impacts to disintegration.
He has demonstrated regenerative abilities, once regenerating his entire body from only his severed head, but with great strain. (Due to the loss of mass, he found it necessary to incorporate new matter from sand.) In his early appearances, he could breathe underwater, such as when he encountered Zauriel in the sea of San Francisco. J'onn also possesses nine senses compared to humans, giving him clearer and more numerable perceptions.
Aside from his superhuman powers, J'onn is also a very capable detective. As Batman mentions in his file, "in many ways, Martian Manhunter is like an amalgam of Superman and the Dark Knight himself".
