Big Peanut Butter is a one-time villain from the 2016 reboot of the Cartoon Network animated series The Powerpuff Girls, only appearing in the episode "Checkin' Out". He is a detective style jar of peanut butter, who only exists in Buttercup's imagination.
Buttercup went shopping for jelly, but when she got to the aisle that normally contained jelly, the jelly was gone and all that was left was a sign that said that the jelly had been moved. Buttercup started picturing everything as a black and white noir detective movie, as she set off on her journey to find out where the jelly had disappeared off to.
Along her journey to find the missing jelly jar, she saw a thief, hidden in a fedora and trench coat, sneakily but quickly, leaving a back alley doorway. Buttercup chased after him and caught up with him, discovering who he truly was. He was the notorious Big Peanut Butter and he explained that he stole the jelly because he was jealous of the fact that Buttercup was buying it instead of him. Buttercup tried to appeal to reason and tell him that she did not need peanut butter for the recipe she was making but he just did not listen.
Big Peanut Butter summoned a mob of his gangsters to attack Buttercup and they put up a fight. Buttercup knocked every single one of them out but after she was done, Big Peanut Butter did not let her have the last laugh and he threw the jar of jelly across the room, causing it to shatter upon impact on the floor. Buttercup tried to stuff the jelly back into the jar but it was no use. The damage was fatal. She began to cry, mourning the loss of her dear friend, as Big Peanut Butter laughed victoriously and fled the scene.
This entire thing was all happening in Buttercup's imagination, meaning that Big Peanut Butter did not exist. In reality, she was just rolling around on the floor, crying over a broken jar of jelly, which most likely broke because she dropped it. These kinds of antics led to her getting kicked out of the store.