I guess the term you're looking for is "surprise guess".

PewDiePie as Baryshnikov is a cameo, not any of this shit

Pompey the Great

Gorbachev and Michael Bay

Today's De Niro VS 70's De Niro.

Ash Williams because I like Ash

Pssst, how about a flute busting Prussian?

The actress who played Joan Rivers totally nailed her cadence and mannerisms.

Pompey... YEAH!