Found this a while ago by accident in EX-1-4 (the bullet room) and was totally baffled. For no apparent reason while I was spin kicking while climbing a vine, suddenly Yuuka's jump arc was noticeably larger and she moved much faster. Thankfully I record whenever I'm practicing so I have a clip of it. I put it beside a regular spin kick for comparison (glitch on the right).

I spent a few days trying to replicate it with no success, wracking my brain, but eventually I tracked down what happened. Yuukarin is coded in Pixel Game Maker MV, and there is a known bug in the engine where FPS spikes can cause velocity to be miscalculated. Reading through their change logs, it looks like they've been trying to solve the issue for a couple years now. Given how long this bug has been around, I expect it's in other Pixel Game Maker MV games as well (such as Luna Nights).

So it seems like my PC lagged while spawning all the objects in the room--since bullets are spawned even when they are slightly off-screen--which caused a very brief FPS spike, leading to the increased distance on the spin kick. This also explains why I had so much trouble replicating it.

Experimenting with throttling my PC, I couldn't get much that seemed useful, nor could I find anything useful from fixing the game's FPS. Also, running the whole game at a lower FPS with graphics cards settings just made everything slower. I think this might be some form of V-sync but I'm not knowledgeable enough on that to say.

Trying to figure out if this would EVER be useful, I used a hack to change the FPS without slowing the whole game down. Sure enough at lower FPS values Yuuka's movement changes, and notably her dash distance goes farther. It also renders her on fewer frames, allowing her to clip through some objects. Here you can see she's moving fast enough to clip through the Autoscroll Start event in one of the later rooms of 3-2, and also clips through the damage event on top of the lava.

However, again this is a hack, and I don't know of any way of recreating this with an unmodified game, so this is still in the realm of theorycraft. If we COULD replicate it, though, it would save a ton of time on 3-2, which would be welcome because it's the longest level in the game and mostly unchallenging.

Finally, FPS drops can actually be a real problem as well. Using this strat for EX-1-4, it feels pretty consistent EXCEPT if the game dips below 60FPS at all, the strat fails. The jumps are so tight that if Yuuka slows down at all she can't make it. My PC is pretty decent so I found it weird that I'm dropping frames at all, especially since task manager says my system isn't taxed at all while doing this, but my GPU is kind of garbo so maybe it's just my machine.

I didn't go for this strat in my submitted run because it's just so inconsistent and it's right before the Kutaka checkpoint, so screwing it up is really costly.

I'm not really sure what to do about this sort of thing, since there's no real standard for PCs. It also feels like throttling your PC with an outside program should count as tool assistance, but on the other hand if the game is lagging because your PC isn't beefy and you're recording with OBS, it seems hard to standardize runs being at the same FPS.

Not sure if anyone will even read this because so few people run this game, but I figured it's worth posting anyways.