What’s most impressive about albatross spawning mutant? (8)
I believe the answer is:
wingspan
'what's most impressive about albatross' is the definition.
(albatrosses have the widest wingspan on Earth)
'spawning mutant?' is the wordplay.
'mutant?' is an anagram indicator (I've seen 'mutant' mean this).
'spawning' is an anagram of 'WINGSPAN'.
(Other definitions for wingspan that I've seen before include "Lateral spread of an aircraft" , "Distance between the extremites of a bird or plane" , "Linear distance across a gliding bird" , "Aircraft's overall width" , "fighter's reach, maybe" .)