Galactus possesses cosmic power beyond most forms of measurement (The Power Cosmic). He can levitate; restructure molecules; convert matter into energy and vice-versa; project energy with enormous concussive force; teleport himself, others, and objects across space, dimensions, and time; erect virtually impenetrable fields; restore others from any injury, even total disintegration; and endow or enhance powers within others. Even his heralds, imbued with the smallest fraction of his power, can manipulate matter and energy far beyond human comprehension. Though he generally avoids physical conflict, Galactus can bolster his own strength beyond any known system of measure. Galactus is telepathic, able to scan the thoughts of virtually any known being.
To sustain his immense power, Galactus requires energies derived from a biosphere, a planet able to sustain living beings, though life does not actually have to be present. Though Galactus can extract and absorb this energy himself, he generally employs his immense Elemental Converter to perform the process, as it is far more efficient and avoids the expenditure required of him. Sometimes the planets on which he feeds are left barely habitable; other times he consumes all life and water, leaving it devastated and barren; most often the process reduces the planet to space rubble. When Galactus was newly formed, the energy of a medium-size Earth-like planet sustained him for over a century. Now he needs to feed about once a month; in addition, when preparing for a massive expenditure of energy, he may absorb planets more frequently to amplify his power stores. Conversely, when he does not feed within his allotted time, his energies will dwindle, and he will even begin to physically shrink as they drop dangerously low. His body totally converts the energies he absorbs for his life functions and activities without any waste products.
Though seemingly destroyed on several occasions, Galactus is always restored to full power eventually. In addition, despite being a physical being, Galactus can adopt a manifestation (M-Body) from the Dimension of Manifestations in order to commune with abstract beings, such as Death and Eternity.
http://marvel.com/universe/Galactus
He is a being of power unimaginable to mere mortals. The very sight of him drives mortals mad. On 2012, at the rise of the Gibbous moon, on the end of the Mayan Calendar, he will awaken from his slumber and teach man a new kind of fear. He will arise from the lost city R'lyeh in the furthest Reaches of the sea. His spawn are the foul deep ones, smaller versions of the great one and the people of the lost city of R'Yeh. A place with structures built with non-euclidean geometry, the very likes of which cannot be imagined by mere mortals, and to lay eyes on it is to be driven to the depths of Insanity. His cult is centered in Arabia, with members all over the world, from Greenland to Chile. The leaders of the cult hailing from China. Among the Great Old Ones his main rival is his half brother Hastur.
He has power beyond mortal comprehension and is able to nearly instantly regenerate his body if it is ever to be damaged the wound will heal faster than it is made. He is the ruiner of countless worlds, the devourer of innumerable souls, and ender of hope. He also has immortality beyond what most can comprehend, for it is stated that he will outlast death itself. If this is true then he can never be truly destroyed. He is as large if not larger than any earthly mountain, being able to stand well above sea level in some of the deepest parts of the sea. It is unknown whether or not he can fly using his massive wings, but it is probable. He is also capable of shape shifting, as he has taken multiple forms over the years, one the Octopus headed, Dragon winged, Human caricature that is the most familiar. Another a gigantic pulsing blob of writhing tentacles and mountainous pseudopods. Another a huge mass of constantly changing colors. All will cause a man to go insane upon glancing it.
In fact Cthulhu's power is so tremendous that when he is to awaken everything in 1,000 miles of R'lyeh will either be destroyed in mind, body, and soul which is the fate of the more fortunate ones, or go irrevocably insane as you see the truths of the omniverse. Unlike most beings who are limited to one multiverse, Cthulhu exists in the Dungeons and Dragons multiverse as well as the Lovecraft mythos at the same time. His mastery of magics, technology, and psionics have few equals anywhere in existence and the simple fact that he has mastered all three of these rather than just one is truly a feat. He also is capable of reality, matter, energy, time, and space manipulation on a truly massive scale. His age is stated to be in the vigintillions of years, or 120 or so Zeroes. Thus making him vastly older than the universe is predicted to be or even is predicted to last, thus implying that he has seen many many universes come and go and that ours is merely the latest one to him.
More of his powers include, the ability to ignore nuclear weapons as if they were nothing, knowledge and mastery of every single spell, and much like the vast majority of the great old ones, is able to summon Azathoth with a spell that has the energies to destroy worlds. Azathoth is the ruler of the outer gods, beings above the Great old ones and equals of the Elder gods in the books of August Derleth. His age is in the vigintillions or one followed by 120 zeros.
http://www.comicvine.com/great-cthulhu/29-40994/
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