Update will come later today.
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Spirits just tend to look like blobs of energy, when they take a physical form. They have neither the ability nor imagination to take anything fancier as a form.
Demons can shapeshift to an extent, but they will always have common features between all their forms. A fey will always appear to have features of plants, for example. The more powerful demons also tend to be smarter, so will have more varied and fancy forms.
For example, the demon in your drive - Gottarjang - tends to look like a centipede. Whatever form he takes, it will always have a lot of chitin and legs. He isn't a massively powerful demon, but he is a demon of movement, so he can move the ship around. If you wanted him to take over life support, you'd have to modify the ritual bindings on the drive core and even then he still wouldn't be very good at it. Vice versa with the demon in the life support, Axaspheous, who appears more like fleshy, breathing bubbles. Juts because demons tend to resemble their sphere doesn't mean, however, you can't get curveballs or demons deliberately hiding their nature.
Physically manifesting takes a lot of energy, and demons need energy to exist out the Not-Here. Demons need to be summoned to exist on the material plane. However, poor bindings - or broken ones - in areas with a lot of mana about can become home to stray demons. These would tend to be weak demons like gremlins. You have gremlins on the ship - more precisely, bound into the boots of your void suits so you can walk on the sides of ships, etc. If the suits weren't maintained, the bindings could loosen and the gremlin would get out. Most demons also don't know how to get back, so they'll hang around until either out of power or desummoned. Running out of power is a rather unpleasant experience for them.
Or someone might summon a gremlin in combat, for instance, but drawing a quick ritual circle and placing mana inside it. If the gremlin happened to find enough mana after it did whatever it was bound to do by the summoning, it could persist.
Typically you don't want loose demons running around, since you don't know how malicious they might be, and they're eating your mana.
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For the most part, you can control your drake, but I reserve right to assume direct control of it for suitably dramatic moments, etc.