After a wholesome scene between you and Chicory, she’ll give you the next step of your quest to figure out what is causing the corruption disrupting the world. You will venture to Gulf Swamp, which is south of Luncheon. With your new swimming ability, you’ll be able to get past some trees left of Beans that obstructed your progress. Follow signs that point downward to meet up with Blackberry and continue onward to the swamp.
The trick for navigating Gulf Swamp is using the vines — when painted, you can swim through them to get on different islets. However, as all of these vines twist and turn and are obscured by flora, it may be unclear where a vine begins or ends. Here, you will want to take advantage of the different colors the game has to offer. If you color one end of a vine, it will spread to the rest of the vine. Use different colors to differentiate the vines, assuming you’re able to discern the differences in color; otherwise, perhaps color some but not all. This will make navigation significantly easier.
Your end destination is a large, corrupted tree in the center of the swamp, and you may find yourself stuck in a spot. You will find yourself covering all ground, but unable to get to certain sections and islets due to how the vines are organized, and trees and bushes will block your passage. All will make sense once you find a visually obscured path: go to the house of Shroom, the lone resident of the swamp — from there, move up and notice on the right that there is an extremely thin path that you are able to pass through by swimming in paint. After this, the path to the tree should be clear if you are color-coding the vines.
Inside the tree itself, the only difficult obstacle is finding a pattern for a door with 3×3 dots. To find this pattern, swim through the narrow path on the left and through the vine going to the right and move to the next screen on the right. Use paint to lighten the cave, but keep in mind that there are bugs that will eat away at the light. There are nine little platforms in a 3×3 grid — perhaps you can see where this is going. The vines that connect these platforms go nowhere, but note which platforms have any vines connected to them; fill in the corresponding dots on the 3×3 grid where those vines are to get past the door and to a boss fight.