Voidcrawler (Mycocelium Nocturnis) is a voracious invasive species, most similar to a fungus but much hardier and with some singularly unique properties:
Firstly it absorbs not only light, but also heat from its surroundings and, through processes unknown, both uses the energy to absorb and use nearby materials and stores it as electricity using some strange form of internalised capacitors. As a result Voidcrawler infestations are always dark and cold. The fungal bodies themselves have a near 0 albedo and stay just above 0 degrees Celsius.
Secondly voidcrawler infestations will produce house sized spores that, somewhere in the myriad whorls and twists of their thoroughly inexplicable cellular structures, house a naturally occurring reactionless engine. These spores will eventually, with a bit of a kickstart from their parent body, break away from their parent planet and parent star, accelerating out into the interstellar gulf; feeding on starlight and slowly using up their reserves of stored energy.
When a Voidcrawler spore lands on a planet (they can generally decelerate pretty handily against gravity so they're not impacting at obscene speeds) it almost always spells doom for any species that might live there, eventually rendering the host planet a cold, dark ball that dissolves over the aeons into ever more spores.
The question is this: Given that space is very, very big, and even we (with our telescopes and brains) find it very hard to spot planets around other stars, how do these unintelligent spores navigate to a new star, slow down, navigate to a new planet, and land?
You can assume that concerns about energy, acceleration and continued function in the interstellar void are taken care of.
These aren't your normal button mushrooms.