MBF

MBF (Marine's Best Friend) is a source port created by Lee Killough after he left the Boom team. It is regarded by some as Boom's successor. As with Boom, MBF was limited to running under MS-DOS.

MBF adds several features:


 * Friendly monsters, including single-player helper dogs.
 * Bug fixes, such as a fix for the blockmap limit (MBF includes an internal blockmap builder).
 * A "beta" mode, in which MBF emulates the behaviour of press release beta version of Doom. This includes the version of the BFG9000 included in the beta.
 * Higher-resolution 640x400 screen mode.
 * A means to change the level's sky texture (Linedef action 271).
 * Several new Dehacked thing flags (TOUCHY, BOUNCES, FRIEND) and action functions with parameters (e.g. Spawn, PlaySound, RandomJump).

MBF was originally licensed under the non-free Doom Source License, but Killough has since relicensed his work under the GNU GPL.

MBF formed the basis of the SMMU port by Simon Howard. In 2004 it was ported to Windows with the name WinMBF by Team Eternity.

Bugs
Due to changes in the collision detection algorithms, a respawned or resurrected monster can sometimes become "glued" to another monster or to a wall. This bug propagated into later ports which used the MBF source, such as PrBoom.

Locked doors requiring all three colors of keys, available through generalized linedef types (a feature inherited from Boom), will not open if the player is carrying a yellow skull key no matter how many of the other keys they have. However, they will open if you at least have a blue key or a red key, regardless of type, even if you have no yellow key whatsoever. Thus, levels that use these doors can be completed earlier than intended or impossible to finish depending on how the keys are arranged and what key types are used.