Reptalith

Reptaliths are enormous aliens from the plane of Behemoth.

Physiology
A Reptalith resembles a six-legged, reptilian creature with a massive suckerlike mouth on the end of a trunk as thick as its head. At the base of the trunk is a ring of eighteen tiny black eyes. A Reptalith is 30 meters tall and 75 meters long, and its knobbly black skin has an unknown property rendering it as hard (but not nearly as dense) as electron-degenerate matter. The creature weighs approximately 800 tonnes. A Reptalith's body is shaped like that of a rhinoceros, save for its head, tail and limbs. The tail is thick but barely reaches the ground, and its belly drags on the ground due to its stumpy legs. These legs are 6 meters feet long and have webbed, four-toed feet, perfect for "swimming" through magma. They have a gland that allows them to create unstable Dimensional Rifts, which they use to get to other sources of food when they have depleted a given world (this can backfire; see History). These rifts are thought to make use of magic, allowing them to access any location they can accurately visualize. These "visualizations" amount to nothing more than a sea of molten rock, according to a now-deceased telepathic entity. Elders are more accurate when it comes to this, and are at no risk of arriving inside giant stars (the iron there often fools normal Reptaliths).

Diet
They have an astoundingly efficient digestive system and a diet consisting mainly of magma. Reptaliths excrete vast quantities of volcanic gases and melt rock into magma via an unknown mechanism. Reptaliths feed by melting rock on the surface and burrow into the mantle when food is exhausted.

Reproduction
Reptaliths lay car-sized eggs asexually once per day if fed, which hatch into babies a day later. These infants are full-sized and ready to lay more eggs within a week. This incredibly fast reproductive rate results in the rapid depletion of edible magma on a given planet.

Lifespan
Reptaliths are ageless for an unknown reason, and they are impossible to kill by conventional means. The only things known to kill a Reptalith are starvation (more than a decade without food) and black holes.

History
A Reptalith emerged through a rift beneath Mt. St. Helens in 1980, causing the eruption as a result of its feeding. It was killed when the rift turned inside out and created a microscopic black hole, which devoured the creature and then imploded. A colony of Reptaliths is thought to have emerged beneath Siberia at the end of the Permian period, and were dragged down to the outer core of Earth by an unknown event. Due to a relative scarcity of anything but iron and nickel down there, the colony is thought to now number only a few dozen, and they are not intelligent enough to leave. Reptaliths have devastated several dimensions, and one Reptalith breeds quickly enough to devour a planet's crust and mantle within a year. A few that have lost their colonies have inadvertently arrived at the cores of red supergiants, where they starve due to an inability to move. According to the X0 Entities, Mars is the cooled outer core of a planet devoured by Reptaliths.

Weaknesses
Nickel is not particularly nutritious to Reptaliths, and einsteinium has the same effects on them as cyanide has on humans. Sadly for their foes, einsteinium is artificial and decays rapidly.

Sapience
Reptaliths are sapient, but they are about as intelligent as a two-month-old child. Elders are as intelligent as a two-year-old. Communication is impossible.

Social Structure
Reptaliths gather in colonies centered on an Elder. An Elder is a Reptalith older than a million years, and are distinguished from the rest of their kind by a club tail and their immense size (60 meters tall, 150 meters long, 3500 tonnes). Lone Reptaliths are not uncommon, due to their dimension-hopping and stupidity.

Language
Reptaliths communicate with each other via gamma-ray pulses, which they use to express simple concepts such as "food this way."