One of the most popular root apps for Android is the Xposed Framework, whose modules allow for unlimited customization and tweaking options.
And the developer behind the framework, rovo8, has announced on the XDA forums, that Xposed for Android 6.0 Marshmallow has been released.
Version 76 of Xposed added support to Google’s latest operating system, but the app reportedly caused issues for many users and has been updated a couple of ties already to patch in some bug fixes.
Do note that i one of the modules isn’t working, it is because they may need to be updated individually. And here is a list of all Xposed modules which work on Marshmallow.