You "saw it" as well, right? That's what it means, after all.
Card Strategy & Abilities
:When this unit is placed on , [ & card with "Seraph" in its card name], your opponent chooses two cards each from their hand, rear-guards, and soul, and imprisons them in your Prison. []:During your turn, all of your front row units get +5000 for every two of your opponent's cards imprisoned in your Prison. If ten or more cards are imprisoned, all of your front row units get +1.