Disney Illusion Island takes place in the sprawling land of Monoth. As a Metroidvania title, you'll be tasked with exploring this island, obtaining new abilities, and backtracking to discover new secrets. Disney Illusion Island Fast Travel isn't very clearly explained and obtaining the ability before going back for secrets can save you a lot of time.
Beginning the game with only the ability to walk and jump, you won't have access to a lot. A double jump that lets you make larger leaps, the ability to get caught in updrafts, and for platforms across Monoth will all occur over the course of the game's story. Each ability gives you further access to find the various collectibles in the game. If you're interested in going for 100% completion then you won't want to waste your time during the story backtracking.
How to get the Disney Illusion Island Fast Travel Ability?
After collecting the three Tomes of Knowledge from across Monoth and returning them to The Library you'll have reason once again to visit each of the keepers of the Tomes of Knowledge, those you took on in boss fights. Instead of forcing you to run, climb, or swim all the way back to them the Fast Travel ability will be unlocked.
With Fast Travel enabled you'll be able to use any of the Quick Save points across Monoth, the letterboxes, as Fast Travel points. With such a high density of Fast Travel points in the game returning to previously visited locations is a breeze.
This coupled with your map outline appearing for areas you haven't visited, and seen but not obtained collectibles appearing on your map you can quickly mop up all of the collectibles you're missing.