Celebrities on the East Coast are showing up in force at the premiere for the new "Deadpool & Wolverine" action flick ... but the big takeaway here is a pooch in costume.

The usual suspects like Ryan Reynolds, Hugh Jackman and Blake Lively dressed their best for Monday's event in New York City ... but all eyes were on Dogpool.

The pooch, a Pug and Chinese Crested mix named Peggy, has a part in the movie as Dogpool ... and the pup was decked out in full costume, looking super cute and adorable!!!

Seriously, look at this little doggie ... that tongue is ready for prime time.

Back on the human side of things, the guest list included supermodel Gigi Hadid, rocker Avril Lavigne, comedian Matt Rife, plus Jimmy Fallon and Al Roker.

*NSYNC was well represented ... with boy band members Lance Bass, Joey Fatone, Chris Kirkpatrick and JC Chasez in the house. No Justin Timberlake, but he's about to take his world tour overseas.

The rest of the cast was there too of course ... but Dogpool is definitely stealing their thunder!!!