dc_eldritch:

Slaughter Swamp has seen it's far share of dark deeds even before the place got it's name. A place of dark untapped power that has resulted in the creation of the being known as Solomon Grundy. Such power would would eventually attract someone who wished to use it. But such power does not always wish to be used and can and will try to defend itself.

In a pulse of dark power all of the dead in Slaughter Swamp arose as zombies to defend it. It also sent out a call to bring it's prodigal son home to help.