Am all bent on backing the beast! (5)
I believe the answer is:
Here is my best explanation:
'beast' is the definition.
(I've seen this before)
'am all bent on' is the wordplay.
'bent' indicates anagramming the letters.
'on' indicates putting letters inside (as in clothing \'on\' a person).
'all' with letters rearranged gives 'lla'.
'am' placed within 'lla' is 'LLAMA'.
'backing the' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
(Other definitions for llama that I've seen before include "Wool supplier", "South American transport animal", "Load-carrier", "Long-necked woolly animal", "Even-toed camel relative", "Andean 'camel'", "mammal that chews cud", "Supplier of wool", "Andean beast of burden" and "South American carrier".)