Overview
In the base game, a character can play a member of an alien species, known as a ‘xeno’, by replacing the starting ability of a playbook with the following:
You may spend stress (0-2) to perform an inhuman feat which only members of your species can undertake.
Note that such xeno abilities must be discussed with the GM and likely the rest of the table to determine what the common traits of such a species are. It matters less what those specific abilities are and more that they suit the setting and are balanced.
Xenos retain the special abilities and the starting action dots on the playbook as normal. So basically they replace their character type’s special ability with something only their species can do.
Alternatively, players can of course play a xeno with no mechanical change at all, with only their appearance or nature or cultural heritage being different in game terms to a regular human.
Xeno Abilities
Prior to the first game the xeno will take part in, discuss the specific abilities of the species with the table. Some guidelines are as follows:
0 Stress: These are either constant abilities or adaptations which don’t affect the game significantly. Breathing water. Seeing in the UV spectrum. Having a prehensile tail, multiple eyes, or four arms that work independently. A heightened sense of smell.
1 Stress: These are abilities which aren’t constant, and require a degree of exertion or concentration to maintain or engage. Good candidates are using 0 stress xeno abilities outside of their normal parameters, or pushing them to their limits. A desert xeno pushing their heat immunity to dive into an engine fire without taking damage. An underwater xeno using sonar to try and sense guards down a metal corridor. An animalistic xeno running faster than their prey, or leaping through the branches of a jungle planet.
2 Stress: These abilities tend to be things that humans couldn’t even attempt. If this only enables you to take an action and a roll is still required, take +1d or +1 effect to it (player’s choice). Ripping chains apart through sheer strength. Breathing fire or generating a sleep venom under your claws. A deep-sea xeno using their incredible lung capacity to temporarily ignore the knock-out gas being pumped into the room.
Optional Rule: Any significant weakness which could take you out of a scene or cause great trouble for you (level 2 or 3 harm equivalent) will also generate a gambit for your crew when it comes up in game. This is a good way to simulate certain extreme allergies, issues with atmosphere, and severe social problems or prejudices. Heat sickness. Calcium deprivation that causes you to hunt your crew. Not being able to leave the ship or enter into key areas of a planet without a disguise.
Future Intent
A future iteration would classify these groups a little more, not necessarily listing an exhaustive list of specific aliens, but to create templates from which characters could then specify more detail about their particular type of alien species.
For example, a “lizard-like” species might have a trait related to regeneration—that’s it, that’s their thing, and beyond that the nature of their lizard-like species is up to the player. Particularly powerful abilities might be paired with some kind of drawback, whereas more modest abilities would simply serve to distinguish such xenos from regular humans.
It should be noted that in this setting, humans enjoy an inherent cultural advantage simply because they are the dominant life form. There are some parts of the galaxy where a xeno of any kind simply will not be welcome.