Animal god happy with miracle periodically (9)
I believe the answer is:
marsupial
'animal' is the definition.
(marsupial is a kind of animal)
'god happy with miracle periodically' is the wordplay.
'god' becomes 'mars' (Mars is an example).
'happy' becomes 'up' (I've seen this in other clues).
'with' means one lot of letters go next to another.
'periodically' means one should take alternating letters (letters must be selected 'every so often').
The alternate letters of 'miracle' are 'ial'.
'mars'+'up'+'ial'='MARSUPIAL'
(Other definitions for marsupial that I've seen before include "Joey maybe" , "eg Wallaby" , "Pouched mammal" , "Mammal that carries its young in a pouch" , "Pouched animal" .)