Prerequisite: See below
Reward: Varies
Unlocks: Fast Travel
Nice though it seems, Coral Island clearly has its problems. The polluting company Pufferfish wants to seize control of the community, and it's your job to stave off their ambitions. It appears, too, that something otherworldly plans to help you on your quest to save Coral Island from the machinations of modern man.
It's not entirely clear which quests unlock Mythical Dream. That said, I suspect this quest pops up after you've watched the townsfolk harangue the staff of Pufferfish, as well as after you've spoken to Connor about the Community Center. Once you have triggered it you'll receive a strange dream the next time you go to sleep, and when you wake up you'll receive the quest.
The quest directs you to visit one of the sacred trees scattered around the island and inspect the tablet in front of it. Any of the trees will do, though if you just want to save time the easiest tree to locate is on a rooftop a short walk east of the Community Center, near Ling's Laboratory. Interacting with one of the tablets will cause a bizarre creature to appear, and it will promptly run off. Oooookay then.
Go home and sleep to have another dream. The next day you'll receive a letter from someone named the Chieftain, who will tell you to visit their home, which is to the 'left' of your farm. Head west through your farm - there's a small trail of petals that will guide you - and follow the trail off your property until you see a fallen log on your left. Beyond it is a small ceremonial ground, and the Chieftain will greet you. The Chieftain will unlock your Third Eye, allowing you to read the tablets on the trees.
You're next told to go meet the Goddess, whomever that might be. Travel northeast of Starlet Town and you'll come to a lake. Use the shallows in the north to cross to the temple in the middle of the lake, where you'll witness a cut scene. Something - the goddess? - is here, and it's struggling. You are told to give an offering to help prevent Coral Island from permanently going under. This will unlock a new quest, Temple Offering.
Look around the temple. There are four altars that you can inspect, each of which asks for a series of related items. Three are inactive, but the one on the left can be used to contribute to Offerings. Four of the six Offerings are tied to specific seasons, while the other two are tied to items that you can collect at any time of the year. The easiest Offering to complete is Essential Resources, which requires you to offer up five of any seven of the following items:
- 10 Wood
- 10 Stone
- 10 Fiber
- 10 Sap
- 5 Maple Seeds
- 5 Oak Seeds
- 5 Pine Cones
Giving these items up in offering will appease the Goddess, and in exchange it will grant you a special boon: Fast Travel. You can now use the stone torch holder near the base of the temple, as well as two more elsewhere on the island, to instantly teleport. This will save you a ton of time walking around. (If you complete the Offering above you will also receive a Recycling Machine.) The torch holder is easy to miss at first glance, so keep your eyes open for rising flower petals at its base.
In addition to unlocking Fast Travel you've also now taken the first step in a much larger project: Completing all of the Offerings. They will require you to travel to every inch of Coral Island, collecting items and completing Offerings in exchange for gifts. Check this temple often to see if you have the items necessary to complete an Offering for nice prizes, and hold back seasonal crops so you don't have to wait a whole year for another opportunity to fulfill an Offering.