Most of the illusion embraced by Stone is of a harsh regime (6)
I believe the answer is:
strict
'is of a harsh regime' is the definition.
I can't judge whether this defines the answer.
'most of the illusion embraced by stone' is the wordplay.
'most of' means to remove the last letter.
'the illusion' becomes 'trick' (synonyms).
'embraced' means one lot of letters goes inside another.
'by stone' becomes 'st' (I am not sure about the 'by' bit.).
'trick' with its final letter removed is 'tric'.
'tric' going within 'st' is 'STRICT'.
Can you help me to learn more?
(Other definitions for strict that I've seen before include "Observing exact rules" , "Authoritarian" , "Demanding that rules are observed" , "Rigidly enforced" , "Harsh and severe" .)