Crimea suffering being invaded by hard monster (7)
I believe the answer is:
chimera
'monster' is the definition.
(I know that Chimera is a type of mythical creature)
'crimea suffering being invaded by hard' is the wordplay.
'suffering' is an anagram indicator.
'being invaded by' means one lot of letters goes inside another.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'crimea' with letters rearranged gives 'cimera'.
'cimera' placed around 'h' is 'CHIMERA'.
(Other definitions for chimera that I've seen before include "fake image" , "Illusion" , "Mythological animal; something illusory" , "figment of the imagination" , "fantasy" .)