That final wave of rats was nasty. When it hit me, I had all my ritual sites garrisoned... and I mistakenly moved Mazdi down towards Hexoatl. I thought he was probably out of range of the Skaven, plus even if they were in range for one attack, I could just retreat, right? Cue 3 armies marching next to me... and the fourth charging in and triggering an ambush, so I couldn't flee. Ended up in a 4v1 battle against an unending tide of rats, in an open field, starting in ambush formation (which is to say, no formation at all).
The resulting battle was, hands-down, the most intense battle I've fought in a Total War game. That's including the undermanned defense of Altdorf that ended with me cycle-charging crossbows and a mortar crew to take out an Orc Warboss in melee, with the capture point barely stable at 19 points remaining. That's including the time I got beaten by a Chaos army, they chased me down to finish me off, and Helman Ghorst pulled off the reversal to save himself and send the Chaos remnants packing. Highlights included Mazdamundi soloing a Hellpit Abom in melee, my Cold One Riders smacking 6 units off the field with a mere sliver of health, my four Temple Guard all hitting regen cap thanks to Revivification Crystal charges, and the moshpit that just would. not. end as their melee hordes fought my dinosaurs in the woods and still managed to not overwhelm me. I ended up losing my underleveled Scar Veteran to an early enrage, but otherwise managed to get out with no permanent losses... and wiped the three Skaven units in march stance at the same time.
By contrast, the final battle was a bit of a letdown, but luckily I had my real final battle a few turns earlier at the hands of the Unknown Skaven Clan.