OK... but I still think my idea for creating a frozen prison was a good one.
I'm definitely going to have to use that sometime.
It seems like it's always some kind of magical bars of force, with a dimensional lock, or a pocket dimension (iron flask), etc, holding back the BBEG/demon/elder evil/etc. But why not just freeze him? That seems a lot easier to pull off with lower level magic, and it's cooler... (Yeah, I went there.)