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The green tent (at the top, near the Elves) opens a passage to the last enemy hero (Castle in the Dungeon); the tent is guarded by emerald dragons. There is a one-way portal leading to it (to the island). You can't sail away from or return from the island, and you have to go through the last hero. The dragons are strong. Personally, I defeated them with the help of allied Elves and a leveled-up Elven hero + the Castle's population. But, in the scenario, it is also suggested to sacrifice the liberated Elves. And then there won't be a second strong hero, so what should I do?
In my scenario, there are no tents, islands, Dungeons, and I didn't place any dragons in the editor. My main hero is not an Elf, but a Necromancer. There is nothing related to sacrifices in the tasks.
Check the map name in the game; if it is not called "Path to Light," then it is definitely not my map. Check the forum for the scenario you have. Please, pay more attention next time.