Mister Mxyzptlk, the infamous Impish from the Fifth Dimension, and Superman -- well not really villain, more like nuisance most of the time -- can be sent back home, if he can be forced or tricked to say his own name backwards.
While that might have been a problem in the past, in today's world, basically everybody carries a recording device in the form of a smartphone (and Superman, or rather Clark Kent probably even long ago carried a dictaphone to conduct interviews as a reporter).
When Mxy introduces himself, usually with his name, could him saying his name forward be recorded and just played back backwards (I am sure there's an app for that): what would then be heard would be his voice saying his name backwards. Would that force him back to the Fifth Dimension? Or if the fact that it's played backwards could be detected, what if he would just be recorded saying his own name backwards once and then that recording would get played whenever he shows up aggain to send him straight back.
Has this method of simply using a recording device ever been attempted in the 73 years since the characters introduction? Or does it violate the "rules" how this dimension hopping works?