Okay, I'm still updating at
http://www.geocities.com/ryan_ferneau/Totally_Rad_U.zip because filespace's server is being dumb. But now I've beaten Act 4's boss!
There were a few surprises along the way. I discovered that falling onto the side of a spike makes you pop up on top of it, reducing most of the wait time from getting hurt. I was going to do that a second time, but I needed the extra hit on the boss, and it turned out that that second fall onto spikes only saved 1 frame anyway. It was also lucky that the boss sinks into the ground and does nothing but his crystal toss attack when his health is low, because he was just about to back into me when that happened.
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Hmm, now this is strange... It seems as though taking damage at the first bouncy ball guy in 5-1 makes the first pogo guy not appear.