The circled letters in the puzzle, when read left-to-right and top-to-bottom spell PHANTOMS, which coordinates well with the title "Ghosted," but there is also the matter of the clue at 69A to address. It reads, "Like this puzzle's circled letters vis-à-vis their Across answers" (LOSTINTHESHUFFLE), which makes it seem like something else is going on that I didn't figure out. I'm counting on our esteemed co-blogger, Colum Amory, to explain this aspect of the puzzle. :)
I FWOED at 18D: "What it takes two to do." I entered DUEl even though HEARTRAlE didn't mean anything to me, but as the across was a question-mark clue, I thought maybe I just didn't get it. I did consider the correct answer, DUET /HEARTRATE, but the way the clue was worded, I rejected it. I thought two couldn't really "do" a duet, although I was fine, for some reason, with that same pair "doing" a duel. I may also have been influenced by the next door neighbor EPEE (One-on-one Olympics event).
I enjoyed the puzzle overall. Some clues I liked in particular:
Good name for a botanist? FLORA - I thought of Ferne initially, but this answer is also quite good.
Competitor of Rugby (ETON) - nice twist on an old chestnut.
Hell, informally (SAMHILL) - this is an old favorite from "It's a Wonderful Life" - "What the Sam Hill you yelling for, George?"
In spades (BUTGOOD) - excellent.
Two of diamonds? (SYLLABLES) - my old friend, the self-referential clue!
Friend of Descartes ... or, in English, question pondered by Descartes? (AMI) - Interesting clue.
Makes out? (TAGS) - tricksy.
Dummkopf (ASS) - both are good words.
Pricey-sounding apparel brand? (LACOSTE) - Ha!