The moment fans reaized Jiyeon's teaser wasn't uploaded with the boys they either got real mad at Bighit because the neon sign in their head immediately screamed "MISTREATMENT" meanwhile the more chill part of the fandom was sure something was up about it, theorizing something was special about Jiyeon's teaser, and they were right.
Immediately it seemed off that Jiyeon's teaser started on a happy note and went more dull after the appearance of the masquerade mask. This made fans theorize that she still was running from the boys or disguising herself to be like the boys. Due to how she seemed to run away at the end of the 'Given-Taken' MV, they suspect the boys are either hunting her down or she's spying on them.
Later fans began theorizing on why Jiyeon's dress was red and gold, mainly. They found out that red symbolizes love, passion, strength, sincerity and happiness. But at the same time it could also symbolize danger, evil, violence and blood. So fans initially thought that it meant that once she had a happy and loving relationship with the boy but it turned dangerous and violent at some point, many theorize this is what happened during the 'Given-Taken' MV. Besides that they found out the symbolism of gold, in the eastern world, is strength, evil and sadness. Again this could show that Jiyeon is now trying to stay strong after her relationship with the boys turned evil. Meanwhile other theories go that Jiyeon is actually the evil one out of the eight, and that is the reason the relationship between her and the boys seem tense and as if the boys is hunting her. Many say that if that's the case then we're watching the story unfold for her eyes, where she is painted as the victim, and not the boys.
As for Jiyeon's masquerade mask, they also analyzed what it meant that it was red and gold colored. If a person's masquerade mask is red it shows that they're energetic and vigourous. It also symbolizes dominance, power and attention. Again hinting at Jiyeon actually being the evil one, with how she may have dominated over the boys and is holding the power to paint herself as the victim and not the boys. Meanwhile if a person's masquerade mask is gold it symbolizes illumination and wisdom, as well as meaning that they've earned their place in the world. So that might hint at Jiyeon outsmarting the boys, and because she did that she earned her place in the world.
At the end of the video there was Jiyeon's sentence of "rejoinder la danse macabre". French Engenes was quick to translate this to "join the dance of death". This is often seen in fairytales as a punishment where the cursed has to dance to dead, but it was also an artistic genre of allegory of the late middle ages claiming that "no matter one's station in life, the dance of death unites all". The theory is that Jiyeon invited the boys to join the dance of death resulting in where the boys currently are in a space between life and death, and is trying to revenge themselves on Jiyeon.