In a medium saucepan, combine the caramel, chocolate fudge and condensed milk. Whisk this and stir until it is well warmed and combined. Typically this is about 10-15 minutes.
If you are using the marshmallow cream add that as well and let it mix in. The marshmallow cream gives it more of a S'mores flavor.
Remove from the heat and add in vanilla extract.
Pour into fondue pot.
Note: If your fondue pot is already heated, you can do this mixing in the fondue pot as well instead of the stove top. Also, please note that the ounces of flavorings may very depending on which brand you buy; however, a little more will just make it that much more tasty!