In a merry state, saw scope to include new festive scene (9)
I believe the answer is:
snowscape
'festive scene' is the definition.
(snowy landscape)
'in a merry state saw scope to include new' is the wordplay.
'in a merry state' indicates an anagram (letters in a drunken or merry state).
'to include' is an insertion indicator.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'saw'+'scope'='sawscope'
'sawscope' is an anagram of 'sowscape'.
'sowscape' going around 'n' is 'SNOWSCAPE'.
(Other definitions for snowscape that I've seen before include "Winter view" , "Christmas scene" .)