Since 0.9, Duo was developed with modularity in mind, and rules in particular had to be replaceable. The 0.10 version introduced this capability and proposes two distinct sets of rules. The first one is a large subset of the Unotm rules because it is the most known variant of the Crazy Eights family, and because the Duo card design was based on it. The default rule set however is a variant to these rules, and difference may grow in the future.
(from Uno Card Game Manual)
Once cards are dealt and the deck placed into the draw pile, the top card of the draw pile is turned over to begin a discard pile. The person to the left of the dealer starts play. He has to match the card on the discard pile, either by number/symbol or color. Alternatively, he can put down a Wild card. If the player cannot play a card, he must take one from the draw pile. If the card picked up can be played, he is free to put it straight down. Otherwise, play moves on to the next person in turn.
Players may choose not to play a playable card from their hand. If so, the player must draw a card from the draw pile. If playable, that card can be put down in the same turn, but the player may not use a card from the hand after the draw.
When a player has only one card left, he must yell “UNO”. If he is caught forgetting this, he has to pick up 2 cards from the draw pile. Once a player has no cards left, the hand is over. If the last card played in a hand is a Draw Two or Wild Draw Four card, the next player must draw the 2 or 4 cards respectively. These cards are counted when the points are totalled.
If no player is out of cards by the time the draw pile is depleted, the deck is reshuffled and play continues.
Special Card Effects
- Draw Two Card -The next person to play must draw two cards and miss his turn. This card can only be played on matching colors and other Draw Two cards.
- Reverse Card – Reverses direction of play. The card may only be played on a matching color or on another Reverse card. If this card is turned up at the beginning of play, then additionally the dealer goes first.
- Skip Card – The next player loses his turn. The card may only be played on a matching color or on another Skip card.
- Wild Card – The person playing this card calls for any color to continue the play (including the one currently being played). A Wild card can be played at any time – even if the player has another playable card in the hand. If a Wild card is turned up at the beginning of play, the person to the left of the dealer determines the color and continues to play.
- Wild Draw Four Card – The person who plays it calls the color that continues play. Also, the next player has to pick up 4 cards from the draw pile and miss his turn. Unfortunately, the card can only be played when the player holding it does not have another valid move. A player may choose to bluff and play the card illegally, but he must draw the four cards if caught. If this card is turned up at the beginning of play, it is returned to the deck and another card is picked.
The Unotm subset in Duo
Here are the rules that are not implemented into Duo when choosing the duo rule set.
- If a jocker is the first card returned, another card is immédiately returned.
- A Draw Four card can be played at any moment.
- There is no way to challenge a player to check if he didn’t bluff, or to yell UNO.
Duo Default Rules
Here are the main differences between the Duo rules from the Unotm.
- Draw Two and Wild Draw Four cards can be stacked. The player who should draw the cards has the possibility to put down another card if its symbol matches. In the case of the Wild Draw Four card, he also calls for the color. The next player in turn either also puts down the same card, or must draw all the cards in the pending penalty.
Note that in the current implementation, the dealer is always the human player in the first round. The number of cards dealt to each player is not controlled by the rules either: it is an option proposed to the player at game start.