Theme:   Remember that a quick scan of all the clues often reveals one that is a hint to several others.  Here it’s  56-Across “Apocalyptic Warning or a hint to 20-, 33- and 42-Across.”   In this case the answer to 56-Across is literally true of 20-, 33- and 42-Across.  For 56-Across, think the cartoon stereotype of a crazy guy on a street corner.

A couple specific hints:

________ Pieces:  Mmmmmmmmm.

Smallest Great Lake:  smallest in letters too; no other 4-letter Great Lake.  ARAL was great, and was freshwater, too, but now it’s drying up to nothing.  Remember it, though, it’ll keep showing up in puzzles long after there’s no water in it at all.

Like the street grid of Midtown Manhattan:  Well, I like to think of the answer as “a tessellation by rectangles or parallelepipeds that are not, in general, all congruent to each other,” but maybe that’s just me.

Mail to the wrong address:  The answer sounds like a word someone thinks should mean send to the wrong address, but I don’t think I’ve ever heard anyone actually say this.

Bar next to butter, maybe:  More often, instead of

Pioneer’s direction:  Think American pioneer.

Suggest: 2 words

Munitions depot:  I thought this was a European football team.