The Quest for the Legends

Chapter 34: Return to Cleanwater (commentary)

In this chapter, the gang make their way back to Cleanwater City to gear up for their second legendary battle in a day, I put Alan through the wringer, and I kill an innocent bystander to make everyone feel bad so the chapter will be less boring for me, which is possibly the most brazenly me thing I ever did in this fic.

Yup, "speak of the devil" is a neutral phrase in English, and it's often used jokingly. To be honest, I'd say it's rare to hear it used in a negative way. So the way you used it in this chapter is totally reasonable.