there is a global reverb which effects all programs that you can turn on and off and change some parameters of. there is also a global compressor. i would imagine that the future holds more possibilities for effects both global and program specific (i def am going to look into it).
a mixer section is not really what norns has… there is input and output gain, monitor gain, and a very basic record function (think like recording to the vinyl on an op1). in LEVELS, you record, and those recordings get stored in the tape folder that can be accessed within samplers as well as in play mode in LEVELS if you wanna just hear what you’ve got.
when in mlr you have the option to either record something live into one of four tracks from a norns input (this method is through mlr program, not LEVELS), or you can load a “clip” from norns internal storage, ie the tape folder. and you can do all of this live, even change the reverb settings all very smoothly while mlr plays in the background and grid is working as a controller.
i also just checked and you can have an audio file (like a field recording or long backing track type thing) playing in LEVELS simultaneously with mlr, and i assume any other program!