Popular red Halloween costume (4)

I believe the answer is:

elmo

(Other definitions for elmo that I've seen before include "St ...'s fire, weather phenomenon of coloured glow" , "Sesame Street character - patron saint of sailors (with his own fire)" , "Puppet character" , "Fiery saint" , "St ----'s Fire: aura from electrical discharge" .)

I've seen this clue in The New York Times.

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