After progressing through Super Smash Bros. Ultimate’s adventure mode, World of Light, you should come across an area known as the “Sacred Land.”
This area is riddled with different puzzles that will test your wits and Zelda knowledge if you want to get everything that’s available.
To the right of the map in the foggy Lost Woods-like area, you’ll notice a fighter out of reach near a treasure chest. There’s no distinct path to get to it and the way to reach it isn’t really spelled out for you.
There is a way to find it, though, and it might be simpler than you realize.
There’s a chest near the pond in the center of the foggy area. All you need to do is press A on that open chest and you’ll jump into it, bringing you next to the character (Chrom) that has been out of reach this entire time.
Honestly, we have no idea how people figured out how to get this character casually. He seems to just be in an area all by himself with no paths or distinct ways to get him.
The only clue you have is a lone chest next to him, so how anyone found out that you could jump into the chest near the lake to teleport to that area is beyond us.