The hero returns.

No, only the "portal to the city" scroll. Everything else is prohibited for certain reasons...

and on which mountain do I need to activate the key? I don't understand.

The green one is annoying - you defeat the wandering heroes, and Ossir returns with increased stats by 25%)) that's crazy))

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Stronger than the first or second human army?

Added after 33 seconds
What difficulty is this?

Stronger than both human armies.
Ossir came to me (for the first time) with an army - 1500 nymphs, 1200 dancers, 900 archers, 300 druids, 150 unicorns, about 100 ents, and 40 dragons.
And this is in a war!))

After that, the humans seemed easy.))
And by the way, who is the yellow one (I saw that color in the tavern)? I haven't encountered him yet (it's not dwarves, not humans, not undead)