There are two secret exits to find in Lost Mangroves!
Towards the end of the level are three floating crates with grasshopper like enemies on each one. Hop into the water and begin swimming down into the hole. Use Dixie’s hair to push past the current. A secret exit can be found towards the bottom. Taking this exit will unlock 1-A: Zip-Line Shrine.
When you reach the Slot Machine Barrel, destroy the crate on the right to reveal a spring. This will take you to the last puzzle piece of the level. However, you can also use Cranky’s high jump to reach the right ledge. Here you’ll find an old music recorder and the secret exit! This exit will unlock 1-B: Busted Bayou.