Yes, it is possible to include many characters in 1 slot like this
:
- in the MUGEN character graphics file (*.sff), add the main player, using all standard sprite set numbers (i.e. #0 for stance sprites)
- in the MUGEN character graphics file (*.sff), add 1st first sub-player, using all non-standard sprite set numbers (i.e. #10000's for stance sprites)
- in the MUGEN character graphics file (*.sff), add 2nd second sub-player, using all non-standard sprite set numbers (i.e. #20000's for stance sprites)
- in the MUGEN character graphics file (*.sff), add 3rd third sub-player, using all non-standard sprite set numbers (i.e. #30000's for stance sprites)
-......and so on....
Then, in the MUGEN character animations file (*.air), add all the main player standard animations (i.e. [Begin Action 0] for stance animation), and add all the sub-players non-standard animations (i.e. [Begin Action 10000/20000/30000/.....and so on...] for stance animation)...
Then, in the MUGEN character commands & code files (*.cmd & *.cns), add all the main player standard commands (i.e. Palette#1 for main player and Palette#2 for 1st first sub-player and Palette#3 for 2nd second sub-player,...and so on...) and code (i.e. [Statedef 0] for main player stance code and [Statedef 10000] for 1st first sub-player and [Statedef 20000] for second sub-player, and so on.....)
It looks complicated, yet each sub-player can be made with some same copy&paste job, of course sub-player can be made totally different than one another.....it depends...........have you tried the Mortal Kombat II "MK2 Shang Tsung" mugenized by juano16?
juano16's "MK2 Shang Tsung" (aka main player) makes use of the above MUGEN way to let Shang Tsung be able to transform to more than 12 other MK2 characters (aka sub-players) in-game with different MUGEN input commands, just like what he can in the MK2 source game.
But, such MUGEN transformation has one (1) big flaw -- like, when juano16's "MK2 Shang Tsung" transformed to like Scorpion and when Scorpion was being thrown (i.e. being put into a MUGEN Custom State made by and given by Shang Tsung's MUGEN Enemy/Opponent), only the Shang Tsung (aka the main player)'s would be shown during so.........it happened due to a well-known MUGEN Engine's Custom State control limit.
I have seen some cool MUGEN creators/authors who try hard on a work-around for this well-known MUGEN Engine's Custom State control limit -- 1) detect the main player being put in a MUGEN Custom State by player2/player4 or not; 2) upon detection make the Shang Tsung main player invisible; 3) add a MUGEN Helper Scorpion (some even use a MUGEN Explod aka VFXs) to try its best to imitate/mimic Shang Tsung main player's get-hit states & animation, to try to make a MUGEN illusion that player2/player4 is throwing Scorpion rather than Shang Tsung..........of course the MUGEN result can never be perfect and in some MUGEN cases and sometimes it can look even uglier than the standard Shang Tsung main player's MUGEN Custom State by player2/player4......
Simply put, you can make your MUGEN character to be able to transform to anything in-game, and the only MUGEN concern is when your MUGEN character is being thrown by his/her/its MUGEN Enemy after a transformation......
It is from my MUGEN experience......
....if there is something wrong then please feel free to correct me any time.......