Ooh, ooh! It's a Wednesday rebus puzzle! Bonus!
I figured something was going on when I hit 18A: Marx with a curly wig (HAR[PO]). I then noticed 9D: Dr. Seuss book that introduces phonics (HO[PO]N[PO]P). I initially had just "hoppop" there, thinking it might be a literalization of the title ("hop" on top of "pop"), but then figured out how to make the two puzzle answers work together. After figuring out the trick I was able to retcon the NW corner and figure out what was going on there.
I appreciated the six answers that doubled up on the PO rebuses, particularly [PO]R[PO]ISE and [PO]M[PO]US. It's a good revealer as well, in POBOX, although does anybody else think the PO in this answer should also have been a rebus?
I also liked 44A: Underworld boss? (SATAN) and 49A: Underworld boss (CA[PO]). My favorite clue came at 1D: Something to keep in a band? (TEM[PO]).
I am perhaps less convinced by ARSONS. Is this a term that anyone can actually pluralize? "Yesterday, I committed two arsons." In my humble opinion, I think that would be committing arson twice.
But I don't want to [PO]LLUTE my review with too much negativity. I enjoyed this puzzle a good deal, and give it a nice thumbs up.
How weird is it that ERICA Jong shows up twice in a few days?