Red monster on TV (4)
I believe the answer is:
elmo
'red monster on tv' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for elmo that I've seen before include "Fiery saint" , "Saint whose fire is electric!" , "Puppet character" , "St ----'s Fire: aura from electrical discharge" , "St ...'s fire, weather phenomenon of coloured glow" .)