“Initially, we were going to have him be a different color green, a slightly faded-out green color,” Mr. Bobin said. “But we started doing camera tests, and it became obvious that he wasn’t Kermit.” The filmmakers decided on the same color and same materials as Kermit, but Constantine’s collar is shorter with wider spikes. And their eyes are different.

“Kermit’s eyes are very smiley. Constantine’s eyes are more flat and slightly bending in to create a sort of a frown.” Kermit’s head, without a hand in it, has a more smiling natural position. Constantine’s mouth falls into a natural grimace. The final difference was the mole. “It’s a classic movie trope. Two guys look exactly the same apart from one birthmark or mole. We love working these tropes into Muppet movies, because they play so well.” When Constantine switches with Kermit, he uses green makeup to hide the mole.

Fingertips Are the Tell

In performing Constantine, Mr. Vogel got one important piece of direction from Mr. Bobin: Watch “Octopussy.” That 1983 James Bond film includes General Orlov, considered by Mr. Bobin a quintessential Russian villain. Mr. Vogel embraced that advice in creating Constantine’s thick Russian accent, but sought to build other dimensions.

“I wanted to create a full-fledged character rather than just a goofy impersonation of Kermit,” he said by phone. He worked on Constantine’s accent with a dialect coach. In working the puppet, Mr. Vogel avoided Kermit’s light, airy moves. “We found a way to make him look heavier and more deliberate. He even sits differently than Kermit, more closed off,” he said. In operating Constantine’s hands, he would either have the fingertips steeple in an evil way or drop the arms and move the puppet from side to side, as if he had shoulders, when he walked. For the face, Mr. Vogel noticed that if he wrinkled Constantine into more of a frown, he made him look menacing.