If you playdevil's advocate in a discussion or debate, you express an opinion which you may not agree with but which is very different to what other people have been saying, in order to make the argument more interesting.
devil's advocate in British English
noun
1.
a person who advocates an opposing or unpopular view, often for the sake of argument
2. Roman Catholic Church
the official appointed to put the case against the beatification or canonization of a candidate