Unfortunately I don't have anyone to play with, but this looks like a really solid base for a TTRPG. It feels like you've provided enough detail while leaving it open enough for the FB to have some agency! I do think the Determination Dice could use a little more explanation, especially regarding how they would fit into Combos, but I didn't really notice any other issues. I love that you included enemies and scenarios as I think that makes it much easier for people to jump into. I also like the corruption mechanic, my only feedback would be the possibility of it leading to a lose state for the player in extreme circumstances.
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Thank you so much for your insight. Determination Dice can be used to add to a roll, but do not take place of a roll, so they couldn't be used to ensure that a player can start or continue a combo. I'm glad that you enjoyed the included scenarios and enemies, as I was hoping that others may find it helpful to use as-is or as a source of inspiration. A lose state is an interesting idea. I guess the only reason why I didn't consider it before was because I didn't want players to have another way their character could meet an unfortunate end, but it does make sense to have them completely mutate into a mindless aggressive being.