Since this is open-source fan software, "verified" usually means the APK is signed by the original developers and has not been tampered with by third-party sites injecting ads or malware. Always scan your APK files with an antivirus if you are downloading from a generic "APK mirror" site rather than the official community channels.
The update adds support for "World Levels," allowing players to create cohesive maps rather than just individual stages. super mario maker world engine 400 download verified apk