Story related, can’t be missed.
*** Spoiler - click to reveal *** Scylla is the legendary sea monster that has been trying to kill Kratos. This time, however, Scylla will be killed by Kratos shortly after the volcano starts to erupt. Complete the quick time events underwater and eventually you'll have to rotate the Left Stick button to use the giant Archimedian Screw to drill it through her head. After finally killing the legendary sea monster, your trophy will unlock.
All credit goes to orginal authors at playstationtrophies.org, and this is merely updating truetrophy fans with these guides.
http://www.playstationtrophies.org/game/god-of-war-ghost-of-...