My friends and I came up with a variant of the card game Bullshit tonight that is a total mindfuck (in a good way). The strategy involved in playing this game is off the charts, as is the potential for bluffing.
Gameplay
The setup and rules are the same as normal bullshit with a few key variations. As with normal Bullshit, deal out all 52 cards in the deck. The player (or one of the players) with the most cards goes first. Beginning with aces, that player may discard (face down) any number of putative "aces" between 1 and 4 aces, or they may "pass." The next player then has to discard a number of "aces" between 1 and 4 or pass, and so on. This brings us to the key rule change: namely, the card to be played remains on aces until all players "pass" in a row. Only then does play move on to the twos. You will find it convenient if each player announces the new total number of cards played, such as saying "8 aces" when adding 2 alleged "aces" to 6 previously discarded "aces."
Calling Bullshit
Any player may call "bullshit" on the last cards played. The cards are then turned over and the discard pile is given to whoever lied or guessed wrong, just as in regular Bullshit. However, once "bullshit" is called, whether correct or not, play advances immediately to the next card number, even if not all players have passed in a row on the previous number.
Winning the game
As with regular Bullshit, the game ends when one player successfully discards all of their hand.
Strategy
As you can see, there is much more potential for bluffing in this version of the game. The number of alleged "aces" or "tens" or "jacks" or whatever can easily rise to 10 or 12 before somebody finally calls "bullshit" or all players pass. Players can set traps for other players by passing or bluffing even when they have the cards, or by slow-playing their cards of that number. Players can also orchestrate complex serial bluffs in which some cards are the right cards and others are not.
There is also significantly less luck in the outcome of the game. Players are allowed to pass, meaning that nobody is ever forced to bluff. Indeed, unlike regular Bullshit, where almost everything depends on the hand you are dealt and table position, in this variant almost everything depends on the players' actions and decisions, making the hand dealt and table position nearly irrelevant.
Calling bullshit is a delicate proposition in this version because as certainty increases (because you have some of those cards in your hand), the cost of calling increases as well (because those cards will be orphaned once "bullshit" is called and play moves on to the next number).
Ultimately, victory will go to the player who is best at sniffing out opponents' tells and strategically calling their bluffs, while simultaneously managing their own hand successfully and bluffing judiciously.
This game has many levels and will keep you thinking of moves and counter moves for a very long time. It's like rock paper scissors on steroids with regard to how far the I-know-you-know-that-I-know-that-you-know chain can go.
A Final Word of Warning
This game can be deeply frustrating (due to the uncertainty involved in each decision) but also crazy amounts of fun. If you do decide to inflict this deliciously nasty little card game on your friends, I would very much be interested in hearing your thoughts!