Creature this puma moved across river twice (12)
I believe the answer is:
hippopotamus
'creature' is the definition.
(I've seen this before)
'this puma moved across river twice' is the wordplay.
'moved' indicates an anagram.
'across' means one lot of letters goes inside another.
'river' becomes 'po' (Italian river).
'twice' says to double the letters.
'this'+'puma'='thispuma'
'thispuma' with letters rearranged gives 'hiptamus'.
'po' duplicated is 'popo'.
'hiptamus' placed around 'popo' is 'HIPPOPOTAMUS'.
(Other definitions for hippopotamus that I've seen before include "African ungulate" , "Thick-skinned herbivorous animal of tropical Africa" , "Oppo hams it up (anag)" , "African river beast" , "Large African mammal frequenting rivers" .)