This is a game for an even number of players, around six to twelve, but more should work just fine. (If you wind up with an odd number of players, that’s not an insurmountable problem; one player will just sit out in each round.) You’ll need a number of index cards, one for each player. One of these cards will have a black spot or mark of some kind clearly drawn on it. Shuffle up the cards, and hand one to each player; the players should not know which one of them received the card with the spot. The player who received the mark is the first Invader. Their minds have been corrupted by an alien presence, and they will attempt to similarly infect the other, still human, players.
Each player will write three true things about themselves on the card, in order: Something that should be immediately obvious upon first meeting them, something that would be noticed about them after watching them or talking to them for some time, and something that describes something about their internal life, such as a belief or personal preference. The Invader will do the same, but they will also mark the last item (the internal trait) with an X. This represents their corruption, which will spread through the players as the game progresses.
The game is played as a series of short conversations, just a minute or two each. To begin a round of conversations, someone should set a timer for a minute or so, and the players should break into pairs. Conversations should be held discreetly, so that other players are unlikely to eavesdrop on their content or outcome. Clearly, it is preferable to mix up the conversations thoroughly, so the players should always choose to talk with someone that they haven’t talked with before, if possible. Start the timer, and begin chatting with each other.
There are just a few rules about the conversations. If something related to one of the items on your cards comes up, you must talk about it honestly, as written. However, if one or more of the three statements on your card has an X next to it (as the initial Invader will have) then you must actively try to bring that up in the conversation, and you must lie about what you have written; you are forbidden from telling the truth about that item, and must in fact attempt to mislead the other person as well as possible, no matter how ridiculous it might seem.
So, for example, you may have “I love chocolate!” in the third position, and it is marked with an X on your card. In the course of your conversations, you must make it a point to assert how loathsome you find chocolate to be. Likewise, if you’ve noted down that you’ve never pierced your ears as your second statement, you must be sure to talk about your favorite earrings, even though it may be clear that it’s quite unlikely that you’d be able to wear them.
When the timer sounds after a minute or so, quickly wrap up your conversation, and one person must end with the phrase, “Are you okay?” How the players respond to this question depends on whether they have been infected by the Invader or not. (If a player has one or more Xs on their card, they are now an Invader.) Both players will respond with a gesture at the same time, either an okay sign, or with their index finger pointed like a gun. Humans will make these gestures with their right hands, Invaders with their left.
If you’re a human, and you make an okay sign with your right hand, that means that you think that the other player is still uninfected. If both of you are still fully human, and you both do this, you each get to put a check mark (*not* an X) next to one of the statements on your cards that came up in your conversation, affirming your humanity. If none of the statements on your card came up in conversation, you may not check any in this way. An okay sign has no effect on an Invader other than letting them know that you are human, and think that they are okay.
If a human points their finger like a gun at their conversation partner, that means that they think that they are infected by the Invaders. Pointing at an Invader will force them to remove the topmost X from their card; if they no longer have any items with an X next to them, the corruption has been completely removed from that person, and they are human once again.
However, if they point their finger at another human, they suffer for their false accusation! The human player who points their gun-finger at another human player must cross off one of the statements on their card, and may no longer use that statement in conversation in any way. Additionally, if there were check marks associated with that statement, they are lost as well. If a human player is ever forced to cross off an item that has no check marks next to it, they are immediately removed from the game! Attacking other humans is dangerous business.
If an Invader uses their left hand to point their index finger at the other player, they are attempting to corrupt their conversation partner. Their target marks the lowest unmarked statement on their card with an X. They are now an Invader as well, and must be actively dishonest about that item in future conversations. If the target winds up with all three of their statements X’d out, they have been fully transformed, and may not be corrupted or attacked further. A transformed Invader must reveal themselves as such at the beginning of their conversations; they may discuss the nature of the Invaders with their human partners, taunt or threaten them, or simply continue to creepily pretend to be human, although they are clearly nothing of the sort.
If an Invader chooses to make the okay sign with their left hand at the end of a conversation, they are simply activating some kind of protection. Invaders who do this are not affected by a human pointing at them. This clearly has no effect on other Invaders, other than affirming that you are, in fact, infected with the alien corruption.
The game will continue over a number of rounds equal to the number of starting players. At the end of the game, get together and reveal everybody’s cards, totaling up the check marks for humanity, and the Xs for the Invaders. if there are twice as many check marks at Xs, the humans have enough wherewithal to drive out the Invaders’ corruption. You may briefly narrate how this happens. If, however, there are twice as many Invaded players as there are humans, the Invaders are able to round up the humans like cattle, and bring their alien schemes to completion. Of course, if it is clear at any time there are no longer any Invaders, or that there are no uninfected humans, the appropriate side may be declared winners then and there. Otherwise, play it out to the bitter end, and see which side prevails!