Loathsome fellow with a warty skin (4)
I believe the answer is:
toad
'loathsome fellow' is the definition.
(I've seen this in another clue)
'with a warty skin' is the wordplay.
'with' indicates putting letters inside.
'warty skin' becomes 'tod' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a' put inside 'tod' is 'TOAD'.
Can you help me to learn more?
(Other definitions for toad that I've seen before include "Hateful person; animal" , "Warty creature" , "A loathsome person" , "Froglike animal or repulsive person" , "Tailless amphibian" .)