PS4 and XB1 Users - click the description to find a link to your guide. To unlock debug mode and level select on PC you need to do the following:
1. Complete 16 blue sphere special stages.
2. Go to 'No Save' in Mania Mode and Press W
3. Select Debug Mode to ON.
4. Press and hold Q and A on the 'No Save' Box, keep them held down.
5. Select your level and enjoy!
Xbox One: • Sonic Mania | How To Unlock Debug Mode & L...
PS4: • Sonic Mania | How To Unlock Debug Mode & L...
Q: Enable debug placement mode. Press again to disable.
A: Cycle through the available items.
S: when you have selectes an item monitor - Change the item monitor type.
Arrow Keys: Move the object around.
W: Place currently selected item.
I cannot help with control pad controls, although in theory, if setup correctly, it should be the same as my Xbox or PS4 guides depending on your pad type.