I haven't actually tried it but...You make a container with your player and a dictionary. When the dictionary is created, add 1 key per stat and a default value like
-Add key "Health" , 100
-Add key "Attack" , 5
-Add key "Defense" , 2
and if your player is chosen in the events it'll use the stats in the corresponding dictionary.
Then when you go to save the game you can download all the dictionaries as JSON data into a file or webstorage key and load them later on.
Not sure what the best way to tell the difference between the dictionaries would be though. It might be better to NOT use containers and instead give the player and dictionary an identical variable to compare.