Genre: Platformer or Dungeon Crawler
Main Mechanic: The main character has two main types of attacks, Lethal (sword) and Nonlethal (punch/kick/grapple). Enemies are either Cursed (humanoid-type monsters) or regular (animal-type monsters, etc). Lethal attacks do much more damage early on, and if a Cursed enemy is finished with >50% Lethal damage, they die permanently and do not respawn. Otherwise, they are stunned until the player leaves the area. Regular enemies always respawn. Some Cursed enemies are Boss-level encounters, which must be fought repeatedly if beaten through Nonlethal means.
The Twist: A third type of attack, Soul, is earned 1/3 to 1/2 way through the game. These attacks do not do damage, but instead have a chance of ‘cleansing’ a Cursed enemy and turning them back into a normal human; this chance increases as the enemy’s HP approaches zero. Cleansed enemies do not respawn, and may help the player in subtle ways (either through plot devices, loot, or new abilities).
The Hook: The quality of the ending (and the difficulty of the final boss) depends on how many enemies are cleansed; more cleansings == harder boss and better ending. A player who opts for Lethal attacks early on will have an easier time since the tougher Cursed enemies don’t respawn, but ultimately will end up with less Cursed enemies to cleanse once the Soul attack is attained, and even afterward the player may choose the easy path of killing everything and getting the ‘bad’ ending.
The Story (WIP): A warrior is dispatched to an abandoned village to investigate, and on the way there is accosted by a host of twisted creatures. He fights his way to the village, where a wandering monk stops him from killing one of the creatures. The monk explains that the Cursed are actually the innocent villagers, who must be saved at all costs.
The warrior continues on to a nearby mountain, where he finds an old wizard. The wizard explains that he is responsible for the curse, having accidentally unleashed the evil force from an ancient chalice/crystal/whatever. The warrior is granted the Soul attack type, allowing him to cleanse the villagers and send the evil energy back to the chalice.
With the Soul ability, the warrior travels to several McGuffin locations and (cleanses/kills) villagers. He encounters the monk several times, and learns that the monk is suspicious of the old wizard and thinks he, too, may be cursed. They return to the mountain and use the Soul ability on the wizard himself, revealing him to be a demon in disguise; the demon’s power had been sealed away long ago in the chalice, and when he finally freed it, it spread across the countryside and infected the villagers. The demon fights the warrior, drawing dark energy from the chalice; the more villagers were cleansed, the more power/forms he has. The warrior defeats the demon and seals it inside the chalice.
The ending can be Best (all villagers cleansed, you’re a freakin hero!!), Good (most villagers cleansed, and the demon has been sealed away), Bad (the demon is defeated, but at what cost?), and Worst (no villagers saved, and the warrior claims the chalice as his own).