Everett hydra

An **Everett hydra** is a multidimensional, multitemporal creature that possesses an unbounded number of heads. Everett hydras feed on possible futures by attaching themselves to a universe and extending heads into each new altverse that arises from the Tegmark III many-worlds principle. Considered too insignificant to be an existential threat by higher-tier civilizations, and regularly cleaned out of universes by teams of specialist entities, these creatures are nonetheless fully capable of cancelling out uncountable possible future lives and causing enough destruction to render vast groups of timelines uninhabitable.

## Biology

A hydra's body never manifests in a universe directly and does not have typical physical properties like dimensional extent, mass, or charge. Cosmic entities seeking to slay a hydra generally have to resort to more exotic methods, including memetic attacks, reality-warping duels, or ontological warfare. Its heads, which when manifested are typically several megaparsecs long, are configured to think together (while outside of a universe) or independently (while feeding), and while they are totally noninteractive with EM radiation and gravity, they are in theory vulnerable to attack at quantum scales, especially of the sort that causes distortion of the waveforms and prevents the many-worlds splitting from occurring.

While Everett hydras can only be truly killed from outside, heads embedded in a universe can be removed; however, splitting timelines from removal attempts can create new altverses containing *additional* heads. Generally, the only way to rid a timeline branch of a hydra from inside it is to ensure that almost every possible course of events ends in the universe's destruction, coercing the hydra to retreat into the few useful futures, and then attempting to kill it there.

## Behavior

Everett hydras are drawn to universes of high complexity, particularly those incorporating quantum mechanical patterns that allow for their rapid proliferation. Upon locating a suitable meal, a hydra waits in ambush in interuniversal space until one of its branches experiences an event that splits its timeline drastically (say, the detonation or failure of a superweapon, or the intrusion of another entity), and then stealthily inserts its first head into one of the branches in the chaos, causing more branches to bud off and allow further entry. Once anchored in this way, an Everett hydra's head cannot move or swap timelines, but if a head decides that a particular altverse's futures do not have enough potential for the next heads to be useful, it will outright consume all of the futures at once by activating a potent reality-warping effect in its brain, ending the altverse and all of its chronological descendants in one action and converting their spacetime and substrates into material for growth.

An Everett hydra's heads are therefore constantly making high-level decisions on whether to consume an altverse's futures or whether to allow other heads to enter them and thus bud off new possible timelines for even more consumption potential. Thus, the more coordinated the hydra, the less likely it will be to cut itself off, and the faster it can feed.

In an emergency, the hydra can withdraw all of its heads at once, leaving behind no trace of its presence except for a set of timelines which mysteriously failed to occur.

## Life Cycle and Anomalies

In order to reproduce, two Everett hydras must each insert a head into the exact same timeline branch of the same universe; this occurs frequently during "feeding frenzies" involving multiple hydras. A joint feeding by the two - albeit with a bit of communication beforehand to arrange the mating process - allows a transfer of information as the set of futures collapse, carrying the memetic DNA needed to create an offspring.

Alternatively, a hydra can reproduce by entering a spaghettiverse, where the alterations to its own head-insertions can create heads distinct from the hydra that spawned them. This extra head does not need a body in order to contribute memetic DNA, and given the infinite number of them present in a sufficiently tangled spaghettiverse, it allows for infinite proliferation of hydras that often begin competing for resources.