The Marvel Comics multiverse with all their “What If?” Earths. PL:5. SOURCES: Marvel Comics.
Nature of the MultiverseAccording to Forge, mutants living on these alternate Earths have lost their powers due to M-Day, as stated in Endangered Species, however, this mass depowering has not been seen in any of Marvel’s current alternate reality publications such as Exiles, the Ultimate titles, Amazing Spider-Girl, the Marvel Adventures titles or GeNext, though it is possible that the issue of time may be related to their exclusion. This was apparently retconned during the “X-Men: Messiah Complex” storyline, where Forge stated that all mutants in possible future timelines were depowered, not in parallel universes.1 This, in addition to A.R.M.O.R.’s observation that Lyra arrived from an alternate reality2 indicates that the topology of the Marvel multiverse is based on new realities branching off from key nodes of a timeline instead of strictly parallel dimensions.
 Other realitiesSee also: List of Marvel Comics dimensions
Not every alternate reality is an entire independent universe, but instead maintain a parisitic relationship to a parent reality. Others can exist outside the multiversal structure altogether.
 Pocket universesCounter-Earth (Heroes Reborn): A pocket dimension where Franklin Richards stored many of Earth’s superheroes after the events surrounding the appearance of Onslaught. Doom saved Counter-Earth from the unstable pocket dimension, and placed it in an alternate orbit of the 616-Earth on the other side of the sun.
The Encroachiverses: A series of universes deemed failures by extremely powerful, unnamed beings; includes the Dimension of Suicide, the Baloney-verse, the 976-verse, the Trashi-verse, the Don’t-Worry-Be-Happy-verse, the Noriega-verse, the Narcissi-verse, the Media-verse, the Puppet-verse, and the Insipiverse.
The Hill: A dangerous pocket dimension used by Mikhail Rasputin after flooding the Morlock tunnels. Rasputin brought all Morlocks to The Hill to raise them in a survival of the fittest mentality. In this dimension time runs several times faster. While in 616 only 1 or 2 years passed more than ten years passed in the Hill. Marrow and the other Gene Nation members grew up in this dimension.
The Microverse: Originally, many microverses existed within the Marvel Multiverse. The most commonly visited is the one containing the regions known as Sub-Atomica and the Micronauts Homeworld.
The Mojoverse: A dimension where all beings are addicted to gladiator-like television programs. Ruled by Mojo and home to Longshot and the X-Babies.
The Negative Zone: Mostly uninhabited, it is a universe parallel to Earth’s with many similarities. One major difference is all matter in the Negative Zone is negatively charged. Negative Zone Prison Alpha is located here. Also the home of Blastaar and Annihilus.
Otherplace: Also known as “Limbo” or “Demonic Limbo”, A magical dimension of demons which were historically ruled by Belasco and was primarily featured in X-Men comics.
The Void: A pocket dimension that exists inside Shaman’s medicine bag.
The Soul Gem: A pocket dimension that exists inside the green infinity gem.
 External realitiesAvalon: Also known as Otherworld, this realm is an access point to the entire Marvel multiverse utilized by the Captain Britain Corps.
The Darkforce Dimension
Limbo: Also known as “True Limbo” or “Temporal Limbo”, Outside of time historically ruled by Immortus and the location to which Rom the Spaceknight banished the Dire Wraiths.
The Panoptichron: Home base of the reality-hopping Exiles, structurally dissimilar but functionally similar to Avalon.