Did I forget to add him? I did, didn't I... woops. Fix'd.
And yes, it's based on Magic, like all of the other games I've done. This particular game is based on the Innistrad set and storyline, which was released about four years ago, if my math (and my memory) is correct. Coincidentally, the next set to be released (sometime this spring) is called Shadows over Innistrad, and is a revisit to the plane of Innistrad. They haven't released any of the story for that set yet.
The abilities of Thalia and Liliana are based entirely of the story for Avacyn Restored, the third (and final) set in the original Innistrad block. Thalia wants to keep the Helvault sealed if at all possible, because opening it would release all the demons that had been painstakingly been sealed there. Liliana wants to get one of those demons (the one named Griselbrand) so she can kill him (because reasons involving a contract she's gotten tired of), and will stop at no lengths to do so.
In the story, Liliana came to Innistrad, poked around, reanimated a few peeps to get information out of them, found out what was going on, and then realized that she had no way to break the Helvault directly. So, the next option was to find somebody who could (happened to be Thalia), and make them open it. Of course, just asking wouldn't work (and isn't Liliana's style anyway), so Liliana decided to exploit Thalia's position and responsibility as a protector of the humans of the town of Thraben. Liliana cast a spell on the townspeeps, paralyzing them, and then raised a bunch of zombies to munch on them. She then gave an ultimatum to Thalia along the lines of "Sunder the Helvault, or you will watch all of your people be eaten by zombies." Thalia, with no choice left, opened the Helvault, and Liliana called off the zombies and went on her way, chasing that demon.
In this game, I've tried to recreate this as closely as possible. Once Liliana thinks she's accumulated enough Zombies, she will say "Hey, if you guys don't do something real soon, you're all going to die." Thalia, then rather than facing instant death of most of the village and almost certain loss of the game, will activate her own ability. Three things happen:
- Liliana's win condition (and those of all the zombies) is instantly fulfilled. Helvault's open, Griselbrand's on the loose, time to go kill a demon.
- All the zombies die before they have a chance to attack, preventing the village from losing instantly.
- A couple of days later, the vampires and werewolves start multiplying like crazy, if there are any left at that point in time. This discourages Thalia from activating her ability unless absolutely necessary.
Make sense?