Completed Human campaign.
The game is still quite brutal, even with all the advancements in quality of life. You don’t intercept a catapult, and half of your army is dead before you know it.
Counterintuitively, putting catapults in the front of your army works surprisingly well. They are rather sturdy, and extra range allows them to counter enemies early.
Funnily enough, I think that the level before last is harder than the final one. Despite tons of enemies, the base in Blackrock Spire is much easier to defend. Last two levels are basically a Water Elemental factory. You just survive until you get them, then spawn as many of them as possible, overwhelming the enemy.
I still find it awesome that they had a unique sprite for the Blackrock Spire.