Our party has opened war on the Drow capital city, with a rag tag army of Moon Warriors, Pirates looking to make a name for themselves, Forest Rangers, and our not quite stable party of an Eladrin Warlock with multiple personalities, a half orc barbarian with Wonder Woman's tiara, a panther-halfling hybrid rogue, a Giant Powered Kobold, and a Yuan-ti/Gobling hybrid Bard against the forces of the Drow Nation. Numbers are not in our favor, especially as our allies from the Wizard City can't arrive until we destroy the giant spider golem the city has.
Combat is rough, so our party's opening gambit...is to throw out an egg in the center of the city that becomes a gargantuan Spawn of the World Serpent, then run back to our battle. It spawns with only the golem between it and the Arcane Academy, and next to a giant spider nest spawning giant demon spiders once a day.
The first couple days are a bit rough as the tide of battle is not with us, and the serpent, while destroying a large area of downtown, is taking a lot of damage and missing it's attacks on the mechanical and demonic spiders...
So we throw two more eggs into the mess, and continue on with our battle as the Pirates manage to reach us where our part of the army had come up from the underground, the eastern front is still rough but sorta even, and the center of town has had a kaijuu battle going for half a week now.
Oh that, so she's been planning this war thing for a while now, it's been the endgame of our current campaign for about 6 years now. I will point out that, as of the war starting, she's actually using two systems.
We have the usual actual D&D battle if the player party actually enters into proper combat, which is largely meant for when we actively move to encounter special units ourselves, which we will be doing next week as we move to try and take out the Countess who heads up the upper markets where slaves are sold.
But most of it thus far as been an overworld strategy game style of battle she worked up for it, where we have units who's HP signifies the number of members in that unit (Barring special units such as our party being one unit, a slime rancher we recruited, the Pirate Queen's crew, etc), and each unit has a set damage number, a set bonus to attack, an AC and a Morale stat, like so-
Moon Warriors-Infantry HP-8 Attack +5 Damage 1 Morale +3 AC 14 Range 1
Slime Rancher-Special HP-10 Attack +7 Damage 1 Morale +2 AC 14 Range 2
Overworld battle is simply attacks of one unit on another, you choose to attack a square in range. For normal units, your damage goes to the least damaged, non special unit in the square (Ala infantry battles), and special units can choose specific targets to press a weakness or go after enemy commander units. If a unit drops below half health, they have to make a morale save or spend the current turn fleeing.
As an example, my party popped up in the middle of the city with our slime rancher and two platoons of Moon Warriors. This means our square had four units. A neighboring square had two Drow units, so our moon warriors attack there and their damage, if they hit, applies to the unit with the least damage, but either the party or the slime rancher can target a specific enemy unit to try and wipe it out with our better range or damage (The party has 3 damage in overworld). This means the infantry battles are more streamlined and the special units can more specifically target weakened units to lessen the number of attacks against our side.
Lastly, at the start of each day is the Tide of Battle roll to determine which side resolves their actions first during the day, with two actions per day (Actions currently are Unit Movement and Unit Attack, other things may become available as things progress)