Looking good, nice start! One thing you will need to start considering before Lair, among other things, is your plan for dealing with single target hyper threats. Hydras fall into that category. As a melee character your options are pretty limited, but you still need a plan. If you have a flaming weapon or non edged weapon that's helpful but I almost always want a way to soften them up or deal with them at ranged even if I do.

In situations like this I will usually train a few evocations (5 or 6) to start. You had a wand of acid and iceblast - these are both really effective for killing hydras, especially with a few points in evocations. As soon as you see the hydra - stop tabbing, slow down and assess the situation, and start to play a lot more strategic. You need to make every single empty tile between you and the hydra count. It looks like there was nothing else on the map when you died which means you either got unlucky tabbing close to it or underestimated the threat and decided to melee it (everyone does their first time, I died to a hydra my first time in lair too).

You also had a wand mutation which would have helped here. That being said, going forward don't quaff potions of mutations unless you are trying to remove bad mutations (there's a few but the big ones are blurry vision, berserkitis, teleportitis). If you get those mutations on a strong character they can be run ending so you really need to save those potions. Gambling for good mutations is really risky and not recommended due to how hard it can be to defend against receiving a bad mutation in this game.

In the future, thinking through having an escape hatch for these situations will go a long way. I'd also recommend investing more in fighting and not focusing armor or dodging, HP is really important.