Mar 20, 2022, 06:0403/20/22
Please don't take this the wrong way, but - unless your roster has changed *significantly* since the last time you posted here, you have absolutely zero chance of doing anything at all in Hydra. I expect you likely wouldn't last much longer than one or two turns against them at the moment.
With that said, you can select the "Boss Guide" button in the Hydra screen to learn more about their abilities.
Here is the link you are looking for: https://hellhades.com/hydra-clan-boss-heads/
Good luck!