here is my short theory. the benefactor could be a werewolf, or any other supernatural being for tht matter, remember the episode in season 3b when the oni were at scotts house & his mom spread the mountain ash to keep the oni from coming in.?! cause all supernatural creatures apparently cnt get thru mountain ash (except scott).?! now in season 4 when lydia was at the lakehouse her mother told her abt her grandmas ashes & how she wnted lydia to be the one to spread it on her 18th birthday.?! her grandmas ashes turned out to be mountain ash. to protect lydia from the benefactor cause she would be a target after all her grandma was a banshee & banshees predict death. so her grandma could hve knwn who the benefactor was long long before she died. jeff davis said the benefactor goes all the way back to season 1 after the hale family fire.
hale family = supernatural
deapool = supernatural hit list
mountain ash = protection from supernatural beings
idk if this made sense but i hope someone understands wht im trying to say