the corrupted polymerization might have some significance
OK, actually looking at Ep170/171 I have to say I'm not as surprised about the Polymerization in 172 getting stained in darkness. What with the amount of Darkness casually Flying Juudai's way bc of Saiou's attacks. I know he had to get over the fear of using poly after the whole Haou Fiasco, and he ended up accepting haou as a part of him when facing Yubel but it makes you wonder. While he seems cool using it again now, I can't help but wonder if, on a subconscious level, he fears using fusion to cause harm to others again And that's why that darkness from the fool latched onto that card, in particular, sensing that subconscious feeling and latching on because it was such a deep subconscious fear. could also have something to do with the contact fusions too since it's a whole thing of "fusion without polymerization" but that could be me looking too into it along with this speculation for all i know it really could've just been the fool spreading things mindlessly but it's nice to think there's a little more to it than that