Add the cream, chocolate candies, chocolate-caramel candies, peanut butter cups and 18 of the mini chocolate bars to a slow cooker. Turn it on high, cover and cook for 30 minutes. Whisk the mixture until smooth.
If the fondue is too thin, add a few more chocolate bars; if it is too thick, pour in up to 1/4 cup more heavy cream. Cover and cook until completely melted and smooth, another 10 minutes. Lower the slow cooker to warm.
Serve the fondue with skewered apples, bananas, pound cake and marshmallows for dipping.