A Xamek is a humanoid entity. They are genderless, faceless, and featureless. Their bodies are wrapped in a sort of encounter suit that have a variety of two-tone color patterns. There is no real rhyme or reason to the patterns, other than being geometric in nature, and always being symmetrical. The entity has what is considered to be a masculine profile; broad shouldered, tall, and well muscled. They speak in a nonsensical manner, mashing together words regardless of meaning, and again, without rhyme or reason. This makes communications with them impossible, the fact that they are exceedingly hostile doesn't help anything.
Who are the Xamek?
Medical examinations of destroyed Xamek are inconclusive. Attempts to capture one have failed, as they seem to have the ability to spontaneously end their own lives. When functional, Xamek can be injured, they show blood and injury. This seems to conflict with accounts of them not needing to breathe, consume food or water, or excrete. They can also survive in hard vacuum, underwater, in extremes of heat and cold, and in toxic environments. They do seem to have limits, and cannot survive above 250 degrees Fahrenheit. Their immunity to cold doesn't seem to have a limit, but exposure to supercooled fluids like liquefied hydrogen or nitrogen can slow them, or cause them to lose extremities. After destruction, the contents of the suit reduce to a hydrosilicate material. Even the suit itself rapidly degenerates.
(Feel free to distribute these among players as rumors)
Option 1 - the Xamek are an extradimensional species who for some reason are drawn into the terrestrial dimension and they are hostile because of this dimension abduction. An alternate motivation is that arcanotech used on Earth has a completely different waste effect on their point of origin and the xamek are dimensional terrorists trying to shut down said technology.
Option 2 - the Xamek are humans from an alternate dimension/timestream and have been sent to destroy certain pieces of arcanotechnology, and they dissolve because they aren't supposed to be captured, preventing Cosmic Era agencies from extrapolating their existence and point of origin.
Option 3 - the Xamek are straight up aliens who are teleporting into dimensional fatigue events to steal human tech, abduct arcanotechnicians, and otherwise sabotage human works, as the Xamek themselves are incapable of developing this tech on their own. They are successful because of their ongoing intelligence theft operations.
Option 4 - The Xamek are energy ghosts, their patterns are fractured amalgamations of people who have been caught up and killed by dimensional fatigue events.
Behavior and Actions
The Xamek appear in groups of 3-5 individuals. There is usually one that acts as a leader, and will take point as they execute their obtuse plans. While openly hostile, the Xamek are organized, tactical, and efficient. They don't kill indiscriminately, seldom cause collateral damage, and their objectives are at times nonsensical. If threatened, they respond with ruthless force, using hand to hand combat, long bladed weapons they seemingly extrude from their own limbs, and very rarely, a high energy 'pistol' that grows from the hand in a similar fashion. They demonstrate intelligence, and can understand all known human languages. While executing their missions, if a group is in a holding or garrison role, they will explore their surroundings, and will show interest in games, recreational equipment, toys, sports equipment, and so forth.
The objectives of the Xamek seemingly have no reason. One appearance might have them hunting down a single cosmic horror. The next, they might hunt down and kill a reflex team, or a group of scientists. Another incursion might seen a twelve individual team appear for a bloody fight to recover... a red desk stapler.
1. The PCs are caught in a Dimensional Fatigue Event and find themselves not just caught in a pocket of Hell, they are being actively pursued by a group of Xamek. They have to escape the DFE and evade their pursuers. What to the Xamek want? A family heirloom from a PC, a random object one of them picked up, a piece of sensitive tech/information, doesn't matter so long as they are chased. Once the Xamek get what they want, they will take it and quickly fall back to an evac point and 'beam out'.
2. While responding to a DFE, a group of Xamek appear and are seemingly friendly, and want to assist the PCs in fixing the DFE be eliminating the cause. Once the event is closed, they will take 'something' or 'someone' and beam out
3. The Xamek show up Predator style, and are hunting monsters emerging from the DFE, and anyone else who gets in their way.