On the eighth day, the Ranger (Melody), who was just bought in the free Tavern on the lands of Chaos, captured the Chaos Fortress (Virdwell), after which Sandro, loaded with artifacts and potions, immediately sailed to the Fortress of Life.

So, you sent Sandro to Chaos, not to Nature, and left Nature for the auxiliary hero, as I suggested before? That's a correct decision. But I didn't quite understand how you technically did it. On the 6th, you set sail, on the 7th, you landed in Chaos. On the 8th, you broke through with Sandro to the Tavern, bought a Nature hero, Sandro got into the boat, and the Nature hero took the Chaos Fortress? Is that correct? You were lucky that the Chaos player didn't have time to buy a hero in the Fortress, but I had to kill two, because I set sail a day later (it turns out to be an important day :). Therefore, I landed in Chaos on the eighth day. And on the 9th, I act differently. According to my plan, the hero bought in the Tavern will get into the boat with the Vampires - they have enough movement points to return there. And Sandro captures the Fortress alone. He will only get into the boat on the 10th day. There is no one to buy in the Fortress anymore.

He also has (Sextant, arrow of pathfinding, 8 mana potions, Expert Ballista, armor, sling, Cross of Valor, shield, two crystals, acid 1, horseshoe, antidote, sword).

I also grabbed a stunning arrow (in the sea, I think, underground).

Solmyr with a Vampire landed on the shore near the Nature Fortress, with them a Fairy and two Ghosts, poison, Expert Ballista, shield, sword, Dispel, and gas. This should be enough to take down Nature :D

When landing, 50 Harpies attack immediately. So, how did you deal with them?
Or did all these goodies remain with you after the battle with them.

Well, how are you doing? How far did Zhel sail?

Well, I'm still fighting for Chaos.