The Quantum Lice family of pests all leech energy from ships and can phase in and out of existence. Particularly hard to get rid of without a quantum shrieker device.

Cheshire elves only appear as a set of hypnotic eyes in our dimension and wreak havoc on the sanity of crew members (they haunt ships).

Machine elves cause electrical disturbances and overload machinery.

Fungal Infestations turn planets/ships toxic to life, and corruption spreads from The Shroud where it slowly corrupts minds and electronics, filling them with negative energy.

The Scarlet is a myth surrounding a fairytale entity known as Voyager Zero. Said to root in people's hearts and control their sense of love. Obviously that one isn't real of course... but in the stories, people say that Voyager Zero is a beautiful sight to behold.