So through other comments I understand what it is, but can someone explain why you couldn't just sit in a bath of cold water, and keep filling it with new cold water as it heats up from your body?

I'll go with Norm Macdonald off the top of my head. Not necessarily my final choice but that'll do for now.

Yeah I love watching speedrunning, seeing how people absolutely master every aspect of the game, and Celeste is one that's particularly fun to watch.