I don't know why you'd do that. They're potent enough alone, and they both have some unique properties that you won't notice if you mix them together. Unless you have alot of experience with them you'll probably trip way too hard. Fly agaric by itself puts me in another world. If you aren't too heavy, 12.5g should be enough for an intense trip with the amanitas. Not sure about the san pedro. Why mix for one giant uncomfortable trip when you could have two nice trips?