Complex sentence: The Outer Planes are also detailed, with layers, and multiple realms possible on each layer; important layers and realms are included in the descriptions of individual Outer Planes, including which gods (here called Powers) make their home there.
Split into simpler sentences: The Outer Planes are also detailed, with their layers and the realms possible on each layer. Important layers and realms are included in the descriptions of individual Outer Planes, including which gods ("Powers") make their home there.