It sounds like you’re looking for a cracked / repack release of MUGEN labeled as “-800 Characters- 400 Stages” from the group SKIDROW.
While MUGEN is a legal, free engine, pre-bundled packs found on pirate sites can carry risks. MUGEN -800 Characters- 400 Stages- SKIDROW
M.U.G.E.N Complete Guide: A comprehensive setup guide available on Scribd covers the engine's structure, adding characters/stages, and modifying screenpacks. It sounds like you’re looking for a cracked
Here’s a helpful breakdown: