The word "sibyllic" is used to describe something that is mysterious, prophetic, or mystical in nature. If you're looking for synonyms to describe something as "most sibyllic," you might consider words like enigmatic, otherworldly, arcane, esoteric, or transcendental. Each of these words suggests an element of mystery or transcendence, which are often associated with prophetic or mystical experiences. Another option might be to use language that emphasizes the ethereal or mystical quality of the thing you're describing. Words like ethereal, celestial, or sublime could be used to convey a similar sense of awe or wonder.