Hi! So cursed hidan mystery can be targetted to one ninja and two random ninjas, ninjas that can be inflicted with tag will be inflicted with tag. The way Cursed Hidan's standard attack works is it hits ninjas that are inflicted with tag. Killer bee (kage treasure ninja)'s mystery causes the targetted ninja to standard attack twice, which allows cursed hidan to standard attack twice and effectively hitting the tagged units twice.

~Jib