Once you get 16 Gold or Silver medals from the Blue Sphere stages, you can access debug mode from the main menu.
First, go to the main menu, highlight the “No Save” option, and bring up the Secrets options. Make sure Debug Mode is enabled. Next, return to the previous menu, making sure “No Save” is still highlighted, and hold down Square and X. This will take you to the level select screen. Pick a level, and once it loads, press Triangle.
Debug mode lets you freely explore the level and place items and power-ups.
While hanging onto a hook switch in Hydro City, enter the following code: Left, Left Left, Right, Right, Up, Up, Up
This will make the level’s boosters play a voice clip when you use them. The voice clip is of the Youtuber Dunkey.
However, an update for the game removed the voice clip for all versions except the Switch version.