Here’s what I got so far
You need to survive an undead invasion for a set amount of time (let’s go with 25 turns), and you have a fraction of that time to prepare a militia and supplies for your group. (5-10 turns).
You start off turn one with only a few units and around 10k gold. You’d rush those units to three rows of buildings for supplies and extra volunteers/mercs before the undead come.
One of the rows would give random free supplies (elixer, anti-toxin, stuff like that), another row would give free volunteers and mercenaries that you can hire, and another row would offer supplies you can buy. The houses in the rows would be randomized to mix things up each playthrough.
By the end of the prep turns, basic undead like revenants and skeletons would go through, and as the game progresses, entombed, revenants with special weapons (poison, sharp), stronger skeletons, mauthe dogs, and maybe even gargoyles would show up too.
The game ends when you survived a specific amount of turns, and there’s a score for how many houses and units you managed to protect. (House entrances instead of being secured would be replaced with breakable walls, and revenants would be allowed to destroy the houses.)
Would probably adjust a few things, but I might work on making this a romhack in the future. Thought I’d see how this sounds first.