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Initially, I stumbled upon the "Archdevil" campaign, but after reading the messages, I discovered that there's a backstory in the form of the "Warrior" campaign. Thanks to the author for their work! The only issue was in the 5th mission, when I visited the prophet, I encountered some kind of bug. The prophet offered two paths, through a portal or through an altar. I chose the altar, and an entrance to a dungeon opened. I went through it, and in a couple of places, the hero stopped on his own (apparently, something was supposed to happen according to the script), but nothing did. In the end, I reloaded and chose the portal. It was said to collect 75 sulfur. But while building the castle, I first decided to upgrade the entire mage tower and obtained the Astral Gate spell. With it, I jumped over the obstacle and easily entered the portal without any sulfur. I don't know if this is a feature or a glitch. And the final battle turned out to be very easy.
Thanks again!