devtrackers.gg
see title
External link →see title
External link →He's not wrong though, AFAIK all of the most recent mystery boxes haven't had previews or announcements prior to release. (usually getting their announcement page posted a number of days after the new league has started)
We previewed the Glimmerwood one the day before Synthesis launched and the Fairgraves one the day before Betrayal launched. I can't say whether it will happen again though :)