Add004 is an add-on for the M.U.G.E.N and I.K.E.M.E.N engines with a variety of features, predominantly with a flexible tag-team system. Along with being a character patching program and lifebar, it also comes with a screenpack. Most characters made for both engines are compatible with the pre-established system, but there are still issues with variable heavy characters.

Gameplay Additions:
Add004 adds a tag system which means when playing simul it overrides the partners controls, you can summon an assist or change partners with other characters. It also gives them a new lifebar along with a extended meter system, depending on what you choose in the config file you can either get your normal level 1's through level 5 or a max meter in blue which seems to deal more damage and allows you to blue parry while the red goes from 50% to maximum, the red maximum meter allows you to red parry which slightly heals you and also do a lot of hypers. You can parry and red parry by going pressing forward right before the opponent lands a hit on you. There is also a guard break mechanic to insure that the character can't guard forever. There are also 3 different versions of Add004 with the primary difference being the lifebars, Bs0 also removes the parry system.