It appears that a chemical, possibly potassium permanganate, was used. Upon contact with water, it swiftly dissolves, turning the water purple and emitting a fog-like effect.
Wow, impressive illusion! I love how you continually innovate with new ideas and narratives. Reflecting on the trick, one potential explanation that comes to my mind is that perhaps the video wasn't entirely prerecorded as claimed, and the final part of the trick could have been dynamically generated. For instance, when the other participant loudly says the number he was thinking about it might have been transcribed by speech-to-text software and seamlessly integrated into the video.
I believe this trick was straightforward. You initially placed a fake at the front of the deck, and then seamlessly removed it along with the other cards.
