Fixed a name for the devil, mostly considering the devil (7)
I believe the answer is:
satanic
'considering the devil' is the definition.
'fixed a name for the devil mostly' is the wordplay.
'fixed' becomes 'sat' (both can mean positioned).
'name for the devil' becomes 'nick' (I've seen this before).
'mostly' means to remove the last letter.
'nick' with its final letter removed is 'nic'.
'sat'+'a'+'nic'='SATANIC'
(Other definitions for satanic that I've seen before include "Devil-like" , "Demonic" , "Hellish" , "Supremely evil" , "Like hell it is" .)