23. Sea
Screen One
Ignore the shopkeeper here and exit out the bottom path to the southwest.
SAFE STRATS: There is a save point you can take for safety if you go out the exit behind the shopkeeper instead. This might be a good idea if you want to practice killing all the enemies in the next rooms with the upcoming invincibility star.
Screens Two and Three
Use the Star in the box and kill most of the enemies in the second screen and third screen by following the path shown below.
NOTE: Getting all of the starslaps is tricky, so you might need to practice this. If you miss the last one, that's okay but you really don't want to miss more than that for the upcoming boss fights. The path below shows the most efficient way to get all of the enemies.
Mario Reaches Level 7 - ATK
Bowser Reaches Level 9 - ATK (Always)
Geno Reaches Level 8 - HP
Mallow Reaches Level 7 - MAG (Always from now on)
Peach Reaches Level 10 - HP
Remaining Screens
Instead of leaving out the west exit after levelling up, head to the upper right exit instead to find a hidden room next to the save point behind the shopkeeper from earlier. Grab the flower and frog coin from the two back chests in this room.
Now head out the southwest exit and keep running southwest. Don't jump in the water in the next cave room.
Once you get outside, jump out southwest into the water as far as you can and use the whirlpool to descend to the floor.
Head left avoiding the blooper to find the entrance to the sunken ship. Jump up the front of the sails to reach the crow's nest at the top, which is actually a "pipe" that you can go down to enter the ship.