From what I understand, if you let a replay play out til the end, it will consistently store a specific RNG value and to that extent, the exact same one. When you then start playing a scene afterwards, the RNG will start out the same. In this example video, the pattern in 4-7 fires it's bullets in exactly the same places.
What I learned from TASing though would suggest to me that this would only be useful for the first photo for at least some RNG-based scenes, as the timing of the photo and the usage of Charge Speed will influence what happens next. So far this only seems useful for the first photo of certain scenes, like 4-7 and 9-7. The pattern changes midrun after taking the first photo.
In practice you'd basically have to make replays where you kill yourself as quick as possible and then test any replay to check whether they give you RNG you want.
There are 3,333 views in 16 videos for Double Spoiler. His channel uploaded 8 hours worth of Double Spoiler videos, roughly 2.11% of the content that KirbyComment has uploaded to YouTube.
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