This is the strategy for the PS2 version from a walkthrough at gamefaqs.
Strategy: |
| -------- |
| To start off, first, make sure that you either press block, or move |
| away when you first here him breaking through the wood ahead, so that |
| you don't get hurt. After that, hold bock until he sticks his head at |
| you, and it hits twice. Then, slash him a couple of times with your |
| Blades of Chaos, then hold the block button again, until you get a |
| chance to attack again. Keep this up, until his life reaches near the |
| two-third mark. At this time, he'll put his head down, and a circle |
| icon will appear above it. When this happens, grab the beast with the |
| circle button, and hit the correct buttons, as are shown on screen. |
| Kratos will start whipping the Hydra into walls, and will end the |
| combo by stabbing it's eye, causing it to retreat for now. |
'-----------------------------------------------------------------------