Playing golf with clients is one way to 'mix business with pleasure'. [=to do something enjoyable that is related to your work]
I accidentally 'mixed up' the two files. [=I put each of the files in the place where the other one should have gone]
He 'got mixed up in' a plan to destroy the government. [=he became involved in a plan to destroy the government]
(..) Mr. and Mrs. Warren, I'm Maurice Grosse. Thank you so much for coming. I believe you're gonna be staying at the Hodgsons' house. Is that right? ED: Always better to be in the mix. MAURICE: Oh, yeah. I agree. - (INDISTINCT CONVERSATIONS) - (BICYCLE BELL RINGS) PEGGY: You didn't have to do this. (..)2016 The Conjuring 2