The word "mercurial" refers to someone or something that is unpredictable, constantly changing, or having rapid shifts in behavior or emotions. Full definition
Chelsea shouldn't be as defensive as Jose Mourinho was that day, and they have the kind of mercurial talent behind the frontman that United wish they had. (latestchelseanews.com)
With a president as mercurial as Trump, it was anyone's guess what would happen during his first State of the Union address. (techcrunch.com)
It's a key picture in a ten - year cycle obsessed with mercurial personality shifts — with sliding effortlessly in and out of various personae according to expediency and whim. (filmfreakcentral.net)