The play received 'mixed' reviews. = The play's reviews were 'mixed'. [=some critics liked the play, while other critics did not]
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]
(..) That should make him more comfortable. Poor Haku. He's had it hard ever since he got here. He just showed up out of nowhere, just like you did. But he got mixed up with Yubaba. He took a job as her apprentice. I warned him it was too dangerous. "Just quit. Go back home," I told him. (..)2001 Spirited Away