this requires counters..
First off.. have some good sprites ready....second, have a cool character select screen, now you make the first counter..
then you make actions like this if you are using 3 characters:
counter=0| set counter 3
counter=1|display character 1 at certain coordinates
counter=2|display character 2 at certain coordinates
counter=3|display character 3 at certain coordinates
counter=4|set counter 1
when -> is pressed|add 1 to counter
when <- is pressed|subtract 1 from counter.
that is the first part.
then if you wanna display stats,
you have to make a blank text object, then when a counter equals a certain value, have it display text you specify in the events editor.
you must make te character counter a global object. and have it in each level.
then you have to make them selectable..if you wanna add a delay from the time you select them, that requires a counter...I bet you can figure that one out.
counter=anyofthe values above
+fire button 1 is pressed|next level
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now this is where it gets tricky. you have to make the sprites global as well..
now make a group in the events editor for one character, (sounds, collisions, etc) and make sure you DONT have it active when the level starts, you can do this by right clicking the group bar.
then you make 2 others for the other chars...
now here's where our friend the counter comes in:
counter=certain value|activate group "name you specify" make other chars stop.
then add anything else that is needed in the level or game. and you'll be set.

and you can do that first part for a level select, menu, etc...
counters are not just put in this thing to count items and time...they have SO many other uses. and they are much easier to use and quicker than a global value or anything else that changes the game.
you got more options, and a cleaner events system.