Twisted remark ultimately, and dark (5)
I believe the answer is:
kinky
'twisted' is the definition.
(thesaurus)
'remark ultimately and dark' is the wordplay.
'ultimately' suggests the final letters.
'and' says to put letters next to each other.
'dark' becomes 'inky' (I've seen this before).
The final letter of 'remark' is 'k'.
'k'+'inky'='KINKY'
(Other definitions for kinky that I've seen before include "Sexually unusual" , "Given to unusual sexual behaviour" , "depraved" , "Strange, eccentric" , "Twisted" .)