CAMPAIGN: Episode 5: SIGIL (aka SI6IL) by John Romero https://www.youtube.com/channel/UCU7u8u0ZmZU67GOLoQ3r-vg "SIGIL™ is a free megawad for the original 1993 DOOM® created by John Romero. It contains nine single-player and nine deathmatch levels. The free megawad will be released in mid- February 2019 and requires players own the original 1993 registered version of DOOM® in order to play. SIGIL™ is the spiritual successor to the fourth episode of DOOM®, and picks up where the original left off.
You can play SIGIL with several modern source ports such as GZDOOM, or the Steam version of DOOM. You must own the original registered DOOM or The Ultimate DOOM to play. SIGIL is playable in Co-operative, Deathmatch, and Single-Player modes. SIGIL is for PC/Mac."