Changing usual partner is weird (12)
I believe the answer is:
supernatural
'weird' is the definition.
('supernatural' can be similar in meaning to 'weird')
'changing usual partner' is the wordplay.
'changing' is an anagram indicator.
'usual'+'partner'='usualpartner'
'usualpartner' with letters rearranged gives 'SUPERNATURAL'.
'is' acts as a link.
(Other definitions for supernatural that I've seen before include "Mysterious" , "Magical; occult" , "Miraculous, magical" , "Psychic" , "Not of this world" .)