MBF, short for Marine's Best Friend, is a port based on Boom in which Lee Killough, in addition to fixing Boom bugs, added many innovations, such as new codepointers, a "beta mode" emulating Doom's press-release beta, an improved AI (enemies are optionally capable of avoiding hazards such as crushers, and act more tactically, coming to the help of their wounded allies, backing off of melee, and avoiding too many to attack the same target so as to reduce the chance of infighting happening), and the helper dogs that gave this port its name.
Other features include:
- Linedef types 271 and 272 to transfer the line's upper texture to tagged sectors as sky; available as one of the effects of Static_Init
- Various bouncing behaviors, different from those of Heretic and Hexen, available through the BounceType property
- The TOUCHY flag
- Many codepointers: A_Detonate, A_Die, A_Mushroom have been integrated to ZDoom. Others can be replicated differently: A_Face and A_Turn with A_SetAngle, A_LineEffect with a direct call to an action special, A_RandomJump with A_Jump, A_Scratch with A_CustomMeleeAttack. A_Turn and A_LineEffect are also available but only for compatibility.
- Support for embedded DeHackEd lumps
MBF was released under both the original Doom Source License and the GPL. This dual-licensing allowed ZDoom to borrow or adapt code from MBF. Several compatibility options allow to use MBF's behavior on a few points.