I didn't realise there was a forum on here. The main source of RNG in 100% are the four boring stones in Level 2 which sit on top of a beam. The fastest way through this section is to cut down the beam and hope that none of the stones fall. I have found a slightly safer but slower way through this section, which relies on a temperamental glitch to get over the gap. Bringing up the item screen while running in a diagonal direction, taking your hands off the movement controls, and closing the item screen causes Tiny to run at an increased speed. It doesn't work reliably (and notably, varies with graphics settings), but allows you to clear that gap and collect the four stones without cutting down the beam at all.

I don't know if there is any interest in this game for speedrunning any longer, but I thought I would just note this down. In general I prefer that games have less categories in order to concentrate competition, but cassettes% could be fun.