Alexei Navalny, the Russian opposition leader, has been doused in bright green liquid by an unknown assailant in the Siberian city of Barnaul.
Mr Navalny tweeted on Monday: "I will be opening a headquarters in Barnaul as if I am from the film The Mask! Cool. Even my teeth are green!"
He was referring to the Hollywood film that features a superhero who wears a green mask.
The green liquid, a common Russian antiseptic that remains on skin for days, was reportedly sprayed in Mr Navalny's face as he went to shake a man's hand.
Mr Navalny is currently traveling around Russia opening headquarters and campaigning to stand in the 2018 presidential elections.
A criminal conviction for fraud officially bars him from running, but supporters say the charges are politically motivated.