It’s a random selection from a weighted list of boons. By default each boon has a weight of 1, gums add 10 to the weight of boons it targets. The number 10 was an educated guess backed up by some real tests as well by @Tonezone in this thread
From personal experience of mass forging it seems accurate. I also got compliments from James about the simulator so it kind of endorses that it’s correct, even though he didn’t outright confirm the math. Should’ve asked now that I think about it
