The Dome of D'Sparil
The Dome of D'Sparil is the third episode of Heretic: Shadow of the Serpent Riders expansion and the final one of the original version. After killing the maulotaurs at The Portals of Chaos in Hell's Maw, Corvus enters a giant portal to an ancient complex at the bottom of an abyssal ocean, protected by gigantic crystal domes and inhabited by many monsters. It is D'Sparil's strongest fortress, for it is where he resides. Aside from D'Sparil and his green chaos serpent, the only new monster introduced is the ophidian.
Levels are themed to look like the interiors of opulent castles and temples. Whereas the common themes of the second episode were lava and ice, the corresponding theme in the third episode is water. Not only does it take place underwater but there also are numerous water pools or canals found inside each dome. Another distinctive feature is the frequent use of an azure mosaic set of textures. In addition to some of the halls in the levels, each regular exit chamber in the episode has its walls textured with it.
The Dome of D'Sparil has a blue sky that presents the four curved pillars of the current dome. Six level songs are reused from the first episode and one from the second. As in Doom, new music is introduced in levels two and three.