In Fantastic Beasts: The Crimes of Grindelwald we see
Newt coming to the square where the Circus was and cast a spell (something similar to Revelio I believe). This allows him to recreate the events that happened on the spot before - even see the people involved and what they were doing.
What the hell was that?!
First, it seems like a very advanced magic - how many people can perform the spell? Aurors? Dumbledore? Why they never use such a cool tool if it's available? Does it mean Newt is incredibly skilled in pretty all fields of magic?
Second, it looks like a Deus ex Machina. Something that could have changed lots of events in Harry Potter Universe, but for some reason it's the only time we see this comes into action. Yet another thing along with Veritaserum and Pensieve that is not used to it's fullest.
There are lots of questions in my post just to show why I find the spell so important. However, the main question is - what was the spell and how difficult it is to perform for a common wizard?