Alien comes to create upset and so on (8)
I believe the answer is:
etcetera
'and so on' is the definition.
('etcetera' can be a synonym of 'and so on')
'alien comes to create upset' is the wordplay.
'alien' becomes 'et' (extra terrestrial).
'comes to' means one lot of letters go next to another.
'upset' indicates an anagram.
'create' is an anagram of 'cetera'.
'et'+'cetera'='ETCETERA'
(Other definitions for etcetera that I've seen before include "And the rest" , "and the like" .)