Group admitting Danish writer ignoring one English fantasy creature (12)
I believe the answer is:
bandersnatch
'fantasy creature' is the definition.
The definition suggests a singular noun which matches the answer.
'group admitting danish writer ignoring one english' is the wordplay.
I cannot quite see how this works, but
'group' could be 'band' (band can mean a group of people) and 'band' is located in the answer.
'one' could be 'a' (a thing is one thing) and 'a' is found in the answer.
'english' could be 'e' (abbreviation) and 'e' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for bandersnatch that I've seen before include "Lewis Carroll''s frumious monster" , "It was 'frumious' in Jabberwocky" .)