Sigil is an episode WAD for Doom and Ultimate Doom that was released in limited editions on May 22, 2019, while the free release appeared on May 31, 2019. It was announced at Doom's 25th anniversary on December 10, 2018 by its designer, John Romero.

Although billed as a megawad with 18 maps, Romero clarified in an interview that each of the nine single-player levels includes a separate deathmatch arena, making it a standard episode. The levels were created using Doom Builder 2.

SIGIL continues from the fourth episode, Thy Flesh Consumed, with the following story line:

"After killing the Spiderdemon at the end of E4M8 (Unto the Cruel), your next stop is Earth — you must save it from hellspawn that is causing unimaginable carnage. But Baphomet glitched the final teleporter with his hidden sigil whose eldritch power brings you to even darker shores of Hell. You fight through this stygian pocket of evil to confront the ultimate harbingers of Satan, then finally return to become Earth’s savior."
? John Romero