Fiery monster in sulphur alarmed an oddball (10)
I believe the answer is:
salamander
'fiery monster' is the definition.
'sulphur alarmed an oddball' is the wordplay.
'sulphur' becomes 's' ('S' can be a synonym of 'sulphur').
'oddball' is an anagram indicator.
'alarmed'+'an'='alarmedan'
'alarmedan' is an anagram of 'alamander'.
's'+'alamander'='SALAMANDER'
'in' acts as a link.
(Other definitions for salamander that I've seen before include "Long-tailed amphibian" , "Tailed amphibian" , "Mythical fire lizard" , "An amphibian; fire spirit" , "Lizard-like creature" .)