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The Shalka were made almost entirely out of lava, possibly making them some kind of magma form, and so they had no set form, though they did appear once as large worm-like creatures with cobra-like frills, but there were also Shalka of different sizes and shapes.
They lived underground, near where lava meets metamorphic rock, breathing in the volcanic air, though Shalka Prime, their leader, was able to speak english and breathe oxygen. They communicated by screaming and use sound as a weapon and a means of controlling “lower alien creatures”, like humans, and to accomplish other tasks.
The Shalka Confederacy spread across a billion worlds, invading planets using meteorites and then linking them to the rest of the empire by wormholes which they converted from black holes. The Shalka used their screams to take over the planets’ beings and make them scream to disrupt the atmosphere and scorch the planet’s surface. With the surface completely charred, it made other species think that the planet’s population had done it themselves, while the Shalka lived comfortably under the earth.