Has anyone figured out which challenger summoning items summon who to battle?

[-Winks] yes, there's two ways to find this out. The fansite SubetaLodge allows you to search their Item Database by their Notes, and their Notes say which challenger is unlocked. The other way is to go to the Useful Battle Threads sticky thread in Battle. There's a thread there that shows you how to unlock all the challengers.

Thanks! Whoops I misread the 'brought back' part there and thought they were new so no one unlocked them yet. xD;; Happy late St. Patricks day btw!! 🤣