Smash Ultimate Lost Woods can be a tricky area to navigate and to actually obtain in the first place. It's one of the more difficult places to traverse and is full of puzzles for players.
This will be the perfect space if you're looking to unlock Chrom.
Smash Ultimate Lost Woods - Large Tree Stump
When you first enter in the Lost Woods foggy area, you'll notice a large tree blocking the path to Young Link. To talk to him, you'll need to talk to the owl statues scattered around the area until one of them gives you directions. Follow those directions until you jump into a lake. This will take you directly to the place to remove the stump.
Smash Ultimate Lost Woods - Unlocking Chrom
If you wander around the Lost Woods, you'll notice a character sitting out of reach near a chest. That's Chrom. There seems to be no path directly to him, but it's quite simple. Go back toward that lake in the middle of the Lost Woods and click the chest. It will make you appear right next to Chrom. Congratulations! You've now unlocked Chrom.
Photo courtesy of Nintendo