Deals with the Devil?

[MarcoPolo]

But Satan usually does not appear under his true form, as that form is hideous beyond all belief.

He might appear as an angel of light, as a deceased relative. Anything but himself.

This was true in the case of Padre Pio, who had to discern his emotions during an apparition. The devil would appear to him in many forms from the Blessed Mother to seductive women. There are lots of resources for this like here. Or check out EWTN’s audio archives and search for “Pio” for a great series by Fr. Andrew Apostoli on Padre Pio.

You can get a lot of info. from any of Fr. Gabriele Amorth’s books on exorcisms and the devil.

Plus check out some of the Catholic Answers Live radio archives and search for episodes with Fr. James LeBar, who is an exorcist and occult expert.