Sorry for describing it badly, firstly you need to click advanced, tick "edit switches and variables", then go to switches and thick everything that doesn't have "on" or "off" in the name, like this image down here for example, this is for another game because I couldn't do it due to an error in my game and I don't have time to fix it rn, but once you have a save in the recollection room (where you can see all the bosses ending scenes) you just tick everything that doesn't have on/off in the name and it should unlock all of them, sadly I don't know a more effective method but thats what I did to get all scenes
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