From publisher blurb:
What is an aggressive ecology? It’s a new type of challenge for your players, a monster with many faces, a web of interrelated challenges that can together form a complex encounter-in-depth. It is a world-building device based upon a magical interrelationship between disparate, yet connected creatures. It is, in short, something not seen before and something not quickly forgotten.
Most aggressive ecologies are of a terrestrial nature, indigenous to a single planet, and found only in a particular location. But some few travel between the planets, hitchhiking on space-faring matter that eventually lands upon a new and unwitting location. The slaver fungus one such aggressive ecology that arrives on a new world via a meteoroid strike, and if conditions are favorable it expands outward from that location, feeding upon the local organic material until it grows large enough to reproduce, sending its exploding spores to the very limits of the atmosphere. In that instant, it becomes a new threat throughout the entire world.
This aggressive ecology presents a terrible challenge to all 1e/OSRIC Player Characters and is easily adaptable to any OSR system. Present your players a new type of challenge, the Aggressive Ecology!