'He wants to be a snake', I declaim (8)
I believe the answer is:
aspirant
'he wants to be a' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'snake i declaim' is the wordplay.
'snake' becomes 'asp' (asp is a kind of snake).
'declaim' becomes 'rant' (I've seen this before).
'asp'+'i'+'rant'='ASPIRANT'
Can you help me to learn more?
(Other definitions for aspirant that I've seen before include "Would-be" , "Hopeful, wannabe" , "One hoping for success" , "Partisan (anag)" , "expressing high ambition?" .)