13A. Article dunked in mercury for a witch (4) A?G. I go for article as AN put in mercury as HG which gives HANG, but why does that = a witch? Grateful for ideas.
I also went with HANG (believing a mistake to have been made), but also toyed with HAGG thinking that in some skewed way the setter may be thinking of chemical elements (AG) as articles.
If anyone's still interested, I emailed MOS & the response was confirmation that an editorial error led to the word 'HAG' being clued, rather than 'HANG', as necessary for the shape of the completed grid.