In celebration of Doom’s 25th anniversary, one of its co-creators has announced a new level pack for the seminal first-person shooter (via Polygon). Sigil, which takes place after the events of Doom’s fourth episode, will be released as a free download in February and features nine single-player and nine multiplayer levels. Two limited edition fan boxes with collectible extras will also be available to purchase.

Sigil is the work of John Romero, who is widely considered to have co-created the original Doom alongside John Carmack in 1993. Romero developed the 25th anniversary mod over the course of two years in his evenings and weekends using Doom Builder 2, a fan-made modding tool used to create and add new levels to the game. In authentic modding style, Sigil will be released as a MEGAWAD file, the same as any other community mod.

In addition to releasing the files for free online, Romero is also releasing two physical versions of the mod which include various collectible extras as well as putting the mod itself onto a USB stick that’s made to look like a 3.5-inch floppy disk. With the $40 standard edition you also get a CD containing an original song written by metal guitarist Buckethead, who agreed for several of his existing songs to be used for background music across the nine levels. Opting for the more expensive Beast Box for $166 gets you a couple of extra collectables including an art print, T-shirt, and a small pewter statue of John Romero’s head on a spike. All versions of the mod will require an original copy of Doom to run.

Sigil takes place after Doom’s fourth episode — which was itself added two years after the game’s original release with 1995’s The Ultimate Doom — and before the events of 1994’s Doom II. More recently,Id Software rebooted the franchise in 2016 with a game of the same name, and is currently developing a sequel Doom Eternal, with a release date that’s to be announced.

The original Doom is widely considered to be one of the most influential games of all time. As well as popularizing the first-person shooter genre (which lead to early FPS games being referred to as ‘Doom-clones’), it also spawned a vibrant modding community which remains active a quarter of a century later — although typically these mods aren’t created by someone who literally worked on the original game.