A rescuer of creatures missing the last animal (4)
I believe the answer is:
anoa
'animal' is the definition.
(anoa is a type of buffalo)
'a rescuer of creatures missing the last' is the wordplay.
'rescuer of creatures' becomes 'Noah' (as in Noah's ark).
'missing the last' means to remove the last letter.
'noah' with its final letter taken off is 'noa'.
'a'+'noa'='ANOA'
(Other definitions for anoa that I've seen before include "Wild ox" , "water-buffalo" .)