Resilience

I like the idea of not running away from the heroes, but defending the castle walls against them more. (Still, thanks to the map author, they inspired me to create a similar map, but specifically focused on defense.)

I believe the author intended the last two scenarios to involve using expendable units to distract the heroes from attacking the castle (capturing which means defeat) – because it's virtually impossible to defeat the gnome (probably the only way is to have a Berserk, Subdue, and Invisibility spell in all stacks from the Dungeon faction, and Sandro's Cloak).