M.U.G.E.N was originally designed for PC. Most "portable" or "mobile" versions you see advertised for iOS are either:
A full build with 340 characters, high-res sprites, and music often exceeds 3.5 GB . Ensure your iOS device has at least 6 GB free (for extraction + temporary files). anime mugen 340 characters download ios portable
Which follow-up would you like?