honestly for isaac most of the base probabilities i just made sense of on paper and they never changed… well they changes if florian made a typo :) like bad luck causing chests to appear more… but for the most part i just eyeballed it and tried to make sense of it logically, no research i just thought about what i felt had more value and assigned %s based on it. i did room difficulty kind of in the same way. i tend to go with what feels right.
and no, i get alot of request about signing XYZ that people own and shipping it back… its a HUGE pain and id worry your copy would get lost in my house or misplaced somehow… its best to not. maybe if you catchs me at gdc or someplace i can sign it or you can buy something from our shop, i sign most stuff in the shop and if you message Danielle she can push me to make it extra special…