They typically begin with concepts and sketches of how they want the game to progress, then use level editing tools (created by Tools Programmers) in their production in order to eliminate the need to alter a lot of code. (game-designschools.com)
Nintendo really pulled out the stops with Super Mario Maker, delivering an accessible level editing tool that still retains a strong sense of depth. (wizarddojo.com)
Super Mario Maker is a comprehensive level editing tool - set that turns the Wii U GamePad into a perfect canvas to draw your own courses. (theguardian.com)