Things to do, and things not to do.
There is a variety of things we can do to keep us sharp. Some dont appear to carry much risk others rather more.
Some examples, PFLs, stalls, steep turns, practice Pan calls (!), but what about fan stops on climb out, steep(ish) turns in IMC or unusual attitudes in IMC, and very low level flying. Then there are the more unusual like practice radio failures with a return to base and switching off the master switch in flight. I always remember an instructor stopping the engine in the downwind and leaving me to get on with the landing, restarting it as we ran along the runway. It came as a hell of a surprise too his "new" student I can tell you.
What do you do, including the more unusual to keep you sharp, what would you do only with a FI aboard and what do you consider too risky in any circumstances?