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]
(..) There's a mollusc. He walks up to... Well, he swims up. Actually, the mollusc isn't moving. He's in one place. And then the sea cucumber... l'm mixed up. There was a mollusc and a sea cucumber. None of them were walking... None of them were walking... Sheldon! Get out of Mr Johanssen's yard now! (..)2003 Finding Nemo