Deadpool, Batman, Spider-Man and Jesus all walk onto a plane ...
No, this ain't the start of the next 'Avengers' movie ... it's the Pittsburgh Pirates' epic costume party on Thursday!!!
The Buccos beat the snot out of the Braves in Pittsburgh in the morning ... and to celebrate -- they threw on their best outfits and hit the airport for their road trip to Milwaukee.
The guys really went all out ... MVP candidate Josh Bell made a hell of a Batman, shortstop Cole Tucker really loved his Frozone costume -- and pitcher Richard Rodriguez dressed up as Jesus.
A bunch of the starting pitchers -- including ace Chris Archer -- went with Ninja Turtles ... and catcher Elias Diaz was a stunning plus-sized Power Ranger.
The winner of the day (besides the Pirates, who are now just 4 games back of the Cubs in the NL Central) ... outfielder Gregory Polanco -- who had an Avatar costume complete with a tail!!!!
You know how superstitious baseball players can be ... so do it again tonight????