Creature arisen, upset after prince cracks eggs (7)
I believe the answer is:
opossum
'creature' is the definition.
(opossum is a kind of creature)
'upset after prince cracks eggs' is the wordplay.
'upset' says the letters should be written backwards.
'after' becomes 'muss' (I can't justify this - if you can you should give a lot more credence to this answer).
'prince' becomes 'p' (abbreviation for prince).
'cracks' means one lot of letters goes inside another (some letters create an opening in the word).
'eggs' becomes 'oo' (visually resembles two eggs).
'p' put inside 'oo' is 'opo'.
'muss'+'opo'='mussopo'
'mussopo' written backwards gives 'OPOSSUM'.
'arisen' is the link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for opossum that I've seen before include "American native" , "US marsupial" , "Tree climber" , "Thick-furred marsupial of the Americas" , "Native of America" .)