As you may know since minecraft 1.8 "Gravestone mod" was splitted on two parts - "Graves"(only graves) and "Extended"(all another content).
This is the second part of the mod, which consist of additional blocks(such as memorials, spawners, skull candles, and e.t.c), structures(cemeteries, undertaker house, catacombs, and e.t.c) and monsters.
This mod requires "Gravestone mod - Graves" for wokr.
Also some of its content available only if "Advanced Fishing" mod is installed.
Visit official site(I'm still working on its content) or minecraft forum for more information.