Our game today is an open world-RPG, full of quests and adventures and your character’s choices and actions have a persistent impact on the world. Raising and lowering your standing with factions, helping or hurting people as you make your way through the world, and lots of character progression.
This game’s gimmick: Your character has a third arm growing out of her right side. You also can’t control it.
Yes, you’ve been cursed with a third arm and it acts independently of you. You don’t know where the arm comes from or what it wants and it refuses to effectively communicate with you. Sure, it will sometimes point at things to guide your attention and can grab or knock on surfaces to try to direct you, but this definitely is not your arm.
You and the arm are attached and it can’t make things too hard for you because it has a vested interest in keeping you alive as its host. If you die, the arm dies too. You don't know who the arm is or what it wants, you’re just both stuck with one another. The arm isn't overtly helpful or antagonistic, it just has its own goals, and part of the game is trying to figure out what they are as you go about your own quests. It would be fun to have some randomization on how “evil” the arm is willing to be, what factions it likes/doesn’t, and what its goals are to keep things fresh and encourage more community participation rather than having one “correct” route for dealing with the arm.
Anything you have on the right side of your belt and backpack, the arm can reach and use (such as grabbing a weapon, using items, giving things away, using items you were saving, etc), so inventory management is kind of important. But if you’re in a bad spot, you want the arm to be able to help out, so you can’t just leave the arm with nothing all the time.
The arm can activate switches, grab things in the environment, and even start fights on its own. The arm doesn't necessarily abide by your choices, so you could be trying to help a character and be nice to the faction, but the arm just flips everybody off or grabs a gun and opens fire on them. Not everybody believes your story about the arm being out of your control, so blaming the arm for its actions won’t get you out of bad situations. If the arm flings a rock at somebody and they whirl around looking for a fight, they’re going to hit you, not the arm.
If you’re mean to the arm, it will act out against you. So if you refuse to help the arm, deny it healing after an injury, etc, the arm will be more likely to get you into fights, frame you for stealing, or goose a barmaid and blame you for it just to watch you suffer.