Said mounted man's combination with mount was hell on earth (9)
I believe the answer is:
nightmare
'hell on earth' is the definition.
'nightmare' can be an answer for 'hell' (thesaurus). I am not sure about the 'on earth' bit.
'said mounted man's combination with mount' is the wordplay.
I cannot quite understand how this works, but
'said' could be 't' (I've seen this in other clues) and 't' is found within the answer.
'man' could be 'mar' and 'mar' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
'was' is the link.
Can you help me to learn more?
(Other definitions for nightmare that I've seen before include "It makes one restless" , "Terrifying dream" , "dreadful experience" , "Scary fantasy while asleep" , "Frightening dream" .)