"...I also seem to remember seeing a stand up somewhere with an inline twist."
Would'nt an inline twist be impossible on a stander? Well not impossible, but incredibly painful. At the start of the element, your head would be about 6 feet above the track, the twist would put your head 6 feet below the track, (assuming the track's height is constant) forcing G's onto your head (shoulder restraint) during the inversion. The nearest thing to an inline twist would be a corkscrew that kept the center of gravity around the rider's waist. The track would not be at a consistant height, like it is on an inverted.
As for Riddler's Revenge, even though it is taller, and faster than Mantis, it does seem to pull less G's, making it a much more comfortable ride. I think that the plot of land that RR is on must be about twice the size as Mantis'. Making the turns and spaces between inversions wider and easier to handle. I find RR to be smoother as well. Word of warning, CraigTCF, and anyone else who has never ridden... Make sure you are standing in a comfortable position when the harnesses lock down. The ops there don't muck around with people in the wrong position. Not 2 seconds after the lock down, the train is dispached.
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Gotta ride 'em all!