They deliver extremely extravagant surprise (5)
I believe the answer is:
upset
'surprise' is the definition.
(I've seen this before)
'they deliver extremely extravagant' is the wordplay.
'they deliver' becomes 'ups' (I've seen this in another clue).
'extremely' means to remove the middle letters (only the extremes of the word are used).
'extravagant' with its middle removed is 'et'.
'ups'+'et'='UPSET'
(Other definitions for upset that I've seen before include "Discomfit" , "Overturn, disturb" , "Make unhappy; disrupt" , "Disturb - spoil" , "Disordered - unexpected defeat" .)