In the end it was him.
Come on, flip the pickle, Morty. You're not gonna regret it. The payoff is huge.
[Morty hesitantly picks up the screwdriver and turns the pickle over. The pickle has Rick's face on it] I turned myself into a pickle, Morty! Boom! Big reveal: I'm a pickle. What do you think about that? I turned myself into a pickle! W-what are you just staring at me for, bro. I turned myself into a pickle, Morty!