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.
There are few aggressive ecologies found in the deep oceans, and only one centered upon the rotting carcass of a fallen whale. A whale fall is an unusual event in and of itself, but occasionally these massive bounties of detrital material land in places that simply cannot sustain natural life of any sort: a negative energy sink. These strange negative energies infuse a whale carcass with unholy power giving unlife, mobility, and malevolence—creating an undead leviathan. But worse, after enough time, the undead leviathan rises to torment the land!
This aggressive ecology presents appropriate challenges for groups of 10th to 25th levels, ranging from the oceans to the land. Present your players a new type of challenge, the Aggressive Ecology!