"Any card—so long as it exists—has a power that is needed."

oh gosh, is this the one where saiou said some crazy line about catching a mummy

That’s the one! Only I translated it a little less literally lol.  He says “miira-gari ga miira ni natta no sa” or “the mummy hunter has become the mummy”, but I translated it as “I went out [to shear a sheep] for wool and came back shorn”; the phrase kinda has a “well I bit off more than I can chew” meaning to it.  Makes sense in context, since it’s in response to how Judai mentioned that Saiou went to him about looking into Darkness.