Sing badly, so bad tune awful, ultimately (5)
I believe the answer is:
yodel
'sing' is the definition.
(I know that yodel is a more specific form of sing)
'badly so bad tune awful ultimately' is the wordplay.
'ultimately' says to take the final letters.
The last letters of 'badly so bad tune awful' are 'YODEL'.
(Other definitions for yodel that I've seen before include "make an off-peak call" , "Sing (Alpine folk music)" , "Sing like some Tyroleans" , "Sing partly falsetto" , "Falsetto singing" .)