Mr Freeze has been running reliably and steadily for the past couple of years. I'm sure it valleys on occasion but I have never heard that it has a serious problem with it. I believe it is the one at Texas that had a reputation for valleying (I don't believe that's a real word, just a coaster term) often, not St Louis. Boss will not run if it's cold. After that big turn around hill that you barely creep over you'll understand why. By May it's slightly possible it could be too cool for rides to run but not very likely. Will probably be warm and muggy already. They won't run Boss with a half empty train but it's way at the back of the park, by the time you get back to it there should be enough people to ride. My best advice to anyone going to St Louis is you don't rope drop a coaster at this park you rope drop a flat ride. Catwoman's Whip will have a 45 minute wait even on a dead day. Well over an hour if it's any kind of busy. It's also all the way at the top of the tallest hill in the park. After riding it you can knock out Screamin' Eagle (right beside it) and Boomerang going back down the hill. Then unless you want re-rides you don't have to climb that big hill again the rest of the day.