I got enough cards to create Iris but when I try to create her Igor says I don't have the requisite material card. The only material card I know about is one in Mu called "Styx" which isn't used for Iris.
I'm wondering if there is a way to tell what material card is needed for a Persona.
Best Answer
There is no in-game way to deduce which persona requires which card, but you can check this FAQ - it explains which material cards are necessary to summon which personae and where they can be found. In Iris' case, the card requires is Rainbow/Seven Color Light found in an item box in Aoba park.