Twist in extremely degenerate shape (6)
I believe the answer is:
deform
'twist' is the definition.
(deforming is a kind of twisting)
'extremely degenerate shape' is the wordplay.
'extremely' means to remove the middle letters.
'shape' becomes 'form' (synonyms).
'degenerate' with its centre taken out is 'de'.
'de'+'form'='DEFORM'
'in' is the link.
(Other definitions for deform that I've seen before include "buckle" , "Put out of shape" , "Misshape" , "Change the shape of" , "Damage" .)