Nothing from Ireland at the foundation in particular is more mischievous (9)
I believe the answer is:
naughtier
'more mischievous' is the definition.
('naughty' can be a synonym of 'mischievous')
'nothing from ireland at the foundation in particular' is the wordplay.
I cannot really see how this works, but
'nothing' could be 'naught' (synonyms) and 'naught' is located in the answer.
'from' could be 'e' (I've seen this in other clues) and 'e' is located in the answer.
'ireland' could be 'ir' (abbreviation for Ireland) and 'ir' is found within the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'is' acts as a link.
Can you help me to learn more?
(Other definitions for naughtier that I've seen before include "Worse" , "more unruly" , "Less well behaved" , "More badly behaved" , "More mischievous" .)