Demon invasion.

EWA, no, the neutral creatures from there are too tough, especially since I'm playing the first version of the Campaigns, where the neutral creatures are completely random.

My development in the first mission after moving to the surface was roughly as follows: before the first caravan, the main goal was to eliminate the wolves at the passage (using a wave/chain/darkness formation during retreats). After the first caravan, I cleared the sawmill + the elemental tower, and cleared as much territory as possible around the castle. The second caravan marked my first real foray, clearing everything up to the first garrison of dwarves. The third caravan was a full-fledged foray, going all the way to killing Hangwul. The fourth caravan involved killing Wulfsten and completing the mission. The portal with the Dark Elves was only dealt with at the very end.

My hero build was as follows: for the first half (the war with the demons), I used Chaos/Charisma/Intelligence/Logistics/Darkness – a build focused on Devil's Strike for quick completion. For the second half, I used Attack/Darkness/Light (with Wrath + Storm and Protection as must-haves)/Logistics (Sharp Mind is a must-have)/Defense or Intelligence, if it dropped.