Hmmm.....I think this is quite a tricky one...
My mum is a total wimp (no offence mumsy) and when we visited she was to scared to ride. So, I went on as a test try. I loved it! Parts of it are creepy and made me a bit jumpy. However, the ride layout is quite tame. The scariest part of the mummy is the fear of it. Fire, AA's and more fire from nowhere!
So, Big Thunder Mountain gets about a 2 out of ten for it's scariness.
Space Mountain gets about a 3-4 and Mummy gets 4-5
Ride it! it's fun!
Only my opinion.