The most common and most likely answer to this crossword clue is the 6 letter word SCYLLA
S
C
Y
L
L
A
More clues leading to the result SCYLLA
- Singer mentioned legendary rock
- Monstrous female, noted Liverpudlian you say?
- Legendary rock singer from Liverpool on vocals
- Colleague’s going west, skirting constant danger to shipping
- Monster, in seconds, caught friend from behind
- Sea monster that’s one of a pair of scallywags
- Mate’s going north, skirting constant danger to shipping
- Legendary monster and accomplice Lewis picked up
- Black singer broadcast as ‘Monster of Rock’
- Partner, extremely chivalrous, rejected Greek nymph
Buddy explains!

The straight part
We know that "Legendary monster" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case legendary monster = scylla.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.