16d: outer part is 3 ("Voodoo"), surrounding [1, (1,1,1)] where the (1,1,1) are "last letters".
To make it work completely I had to consider the clue an &lit, which caused more confusion.
Really enjoyed this one! Think I’m starting to get the hang of these! As well as benefiting from an explanation of the parsing of 16d, could I also get an explanation of the parsing for 4d?