I found a way to glitch boutu so that it skips straight into its 'downed' phase. I submitted a run which should be approved soon but essentially you would want to start shooting during the first phase at the exact spot I was at (the brown spot behind the plant), this somehow glitches out the second phase and for the third phase I haven't found a consistent way to do it but you would have to move back to the same spot for it to work.

I have only done this with rumi, not sure if it will work for other characters.

Edit: The run has been approved

This is amazing. I need to do some experimentation to see if I can replicate it. Have you been able to do so since this run?

I have been able to replicate it multiple times, but the third phase sometimes glitches back to normal before I can kill it which takes up more time. I have figured out that the spot I talked about is definitely what glitches it, not sure why but I think it might be becuz of the start animation for the second and third phase that happens at the very edge of the screen.