Tiny feet, initially remarkably agile (5)
I believe the answer is:
nifty
'agile' is the definition.
(I've seen this before)
'tiny feet initially remarkably' is the wordplay.
'initially' says to take the initial letters.
'remarkably' is an anagram indicator.
The initial letter of 'feet' is 'f'.
'tiny'+'f'='tinyf'
'tinyf' anagrammed gives 'NIFTY'.
(Other definitions for nifty that I've seen before include "Quick - stylish" , "Clever; stylish" , "Stylish, nimble" , "Particularly effective; stylish" , "Smart" .)