Son faces tough challenge — more dangerous than any other (8)
I believe the answer is:
severest
'more dangerous than any other' is the definition.
(severe can mean dangerous)
'son faces tough challenge' is the wordplay.
'faces' says to take the initial letters (I've seen 'face of' mean this).
'tough challenge' becomes 'Everest' (Mount Everest, a challenge for mountaineers).
The initial letter of 'son' is 's'.
's'+'everest'='SEVEREST'
(Other definitions for severest that I've seen before include "Most dangerous" , "Most harsh and punitive" , "Most strict and harsh" , "Most extreme or difficult" .)