PSA: game tells you which maps you need to complete for Dangerous boss

It seems you can always gain access to this boss, you just need to look in the boss area for blue butterflies around a map - this map will have quest megalith to interact with to open the way. It can spawn several tiles away from the boss arena for me it even uncompleted a map in boss area like 3 times each time with megalith because I failed them initially.

https://preview.redd.it/59ief5ynqzmf1.png?width=622&format=png&auto=webp&s=384af217ccefd59a5b88ec3aff9921e1e490071e