Colonel William Guile...and combos; the greatest friends in the world devastate the opponent with ease. This Guile doesn't need to play defensively, instead preferring to get up-close and personal with the opponent using its easy to pull off combos and high damage output; that said, it can be configured to play like its less cheap Street Fighter Alpha 3 counterpart.
Guile is a six-button character not unlike most (if not all) versions of Guile. The key factor that separates this Guile from the others, as well as how Guile appears in official games, is its insane combo potential and large damage output, easily allowing it to take out almost half the opponent's Life just by performing a 10-hit combo. Its Hyper Combos on their own deal large amounts of damage.
Guile is very easy to play as due to how easy it is to rack up large combos with little effort outside of button-mashing, and of course the aforementioned large damage output. Guile still retains its typical Sonic Boom and Flash Kick Specials, but has various new ones implemented as well; the same can be said with its Hypers, though a multitude of Hyper Combos have been introduced, too. Its Power Charge allows Guile to almost always have at least some meter, as the charge speed starts off relatively fast and just keeps increasing, giving its full meter in mere seconds.
Perhaps fortunately, Guile doesn't have an A.I., meaning most of the time it will be stuck in its Power Charge as M.U.G.E.N's default A.I has a tendency to use those types of moves until hit.
On the flip side, N64Mario's Guile has a "SFA3" mode that is activated through choosing any palette from 7-12. The mode removes any of the new Hypers and makes Guile play almost like its Street Fighter Alpha 3 counterpart, subsequently dampening down its combo potential and making it far less effortless to play as.