Does anyone know if I can use Rich's bettercream under fondant? I wnated to try it tomorrow but I don't know if it will work like BC.

I would think it would be way too soft and unstable to use under fondant.

I think bettercream is the same thing as pastry pride or frostin pride. Do not use it under fondant, it will break down the fondant and you will have a mess. I know this from personal experience.