In a sense, exophages represent some of the most dangerous types of cellverses, as they not only move of their own volition but destroy universes that get too close. It is debatable if they can be classified as such because they are not actual Universes but some do classify them as such due to their size alone. Because of that their interiors could easily be classified as a type of Universe, much different from normal ones, but still one. It would probably be classified as a Surreal-verse under the classification of Universes by Similarity.
Exophages are seen as nuisances by other cosmic entities, who regularly eradicate them from their domains like humans exterminate insects or clean off bacteria. However, for even a Type 4.0 Civilization, they are nightmarish entities capable of near limitless destruction.
The most common way Exophages are born is from a universal form of binary fission, obviously on a humongous scale, which can occur when an exophage has gained enough energy and mass to reproduce. Binary fission between exophages can take millions, or billions of years, like a reproduction phase. Some exophages don't reproduce, and continue to gain energy. Exophages don't grow in size, so by consuming more things, the exophage is becoming more dense, thus, when the exophage reaches its Schwarzchild radius, it will collapse into an unfathomably deadly, universe-sized Black hole that will last for eternity since the black hole's hawking radiation has no space to leak into, therefore it is kept within the singularity. These black holes can be deleted, however, advanced civilizations may have the ability to nullify singularities and/or close the tear in reality. Exophages that aren't born from interuniversal binary fission are born from extrauniversal waste, such as Big Boom remnants or possibly remnants from dead or dying universes. Exophages born this way usually mark the start of an exophage family tree. Sometimes, instead of an exophage forming from interuniversal waste, a Big Bang will stop after a few billion years and form into an exophage instead of a living universe. Exophages can also be artificially formed, easily, by extremely advanced civilizations, ones that have the capability to create universes with different laws of physics.
Exophages can die in 4 recorded ways. One way is to burn out. Exophages, if gone for too long without consuming anything, will eventually burn out within a few million years and die. This is rare, but happens in some cases. Another way is to come in contact with another exophage. This event is quite catastrophic, seeing as both exophages will attempt to eat each other, and only one of these massive amoeba will emerge as a victor, and will soon go through a reproduction phase afterward from abruptly consuming such a large amount of mass in such a short amount of time. The newly created exophage will not attack its parent, though. The third way is to have it consume something such as a superweapon, one which is programmed to deconstruct things down to subatomic level, which will make an exophage tear itself apart from the inside out. The final way is to have it literally erased from existence by very powerful beings, or even beings that approach The Omnipotence Hierarchy, such as Hyperman, who often comes into contact with exophages and mercilessly exterminates them, as he sees them as annoyances, as most cosmic entities do.
When an exophage dies, it functions like a Big Boom with less power. The remnants are scattered through interuniversal space.
The exterior membrane of an exophage is a double layer of flexible, somewhat fluid sheets of dimensional fabric, much like the outside of a standard universe, but capable of bending into wavy patterns or extending outwards into pseudopods. To move, an exophage stretches these pseudopods out into the interdimensional void, anchors them, and then drags itself forward at massively FTL velocities. The membrane is capable of contacting and merging with universes, which the exophage will then consume with enzymes constructed of quantum foam and raw concepts like "digestion" and "dismantling".
Exophages, like normal cells, have a nucleus containing genetic material; however, rather than DNA, their genetic code is written at a subatomic scale as cylinders of densely-packed particles and antiparticles.
While not intelligent enough to communicate or otherwise express thoughts, exophages have at least a rudimentary degree of awareness of their surroundings, and will move towards large clusters of universes to eat, or away from eldritch monstrosities and cosmic entities that could harm them.