Nasty urges shrouding start of fair in an ugly manner (10)
I believe the answer is:
gruesomely
'nasty urges shrouding start of fair in an ugly manner' is the definition.
I can't judge whether this definition defines the answer.
'nasty urges shrouding start of fair in' is the wordplay.
'nasty' is an anagram indicator (a nasty or wrong spelling).
'shrouding' becomes 'mely' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'start of' means to remove the last letter.
'fair' becomes 'ok'.
'in' is an insertion indicator.
'ok' with its last letter taken off is 'o'.
'urges' is an anagram of 'grues'.
'grues'+'mely'='gruesmely'
'gruesmely' enclosing 'o' is 'GRUESOMELY'.
Can you help me to learn more?
(Another definition for gruesomely that I've seen is " in a macabre fashion".)