Riddles about Pluto absorbing artist (8)
I believe the answer is:
charades
'riddles about pluto absorbing artist' is the definition.
I can't tell whether this definition defines the answer.
'riddles about pluto absorbing artist' is the wordplay.
'riddles about' becomes 'c' (I can't explain this - if you can you should give a lot more credence to this answer).
'pluto' becomes 'hades' (synonyms).
'absorbing' means one lot of letters goes inside another.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'hades' enclosing 'ra' is 'harades'.
'c'+'harades'='CHARADES'
(Other definitions for charades that I've seen before include "Game in which answers are acted out" , "Miming games" , "Games like this" , "Guessing game where words are acted out" , "Miming parlour game" .)