The Uno deck has 108 cards, some of which are number cards and some are action cards.
Draw 2 and Wild Draw 4 cards have some similar characteristics.
You can place a Draw 2 card on a card of the same color or another Draw 2 card regardless of color. The next player must then draw 2 cards and cannot play as Mattel explains on Twitter:
This rule still applies even if the Draw 2 card is turned over at the beginning of the game. This means the first player would have to draw 2 cards and their turn is skipped.
Uno has made a decision in May 2019, prohibiting Draw 2 cards from being stacked. This means whenever a Draw 2 card is played, the next player has to draw 2 cards from the draw pile and doesn’t get to place a card.
There are 8 Draw 2 cards in a deck of Uno.
The Wild Draw 4 card changes the color in play (or keeps the current color).
The next player draws 4 cards and loses their turn.
If this card is turned over at the beginning of the game, it’s returned to the middle of the draw pile and its effects are canceled.
As with the Draw 2 card, it is forbidden to stack Wild Draw 4 cards.
There are 4 Wild Draw 4 cards in a deck of Uno.
You can play a Wild Draw 4 card only when you have no cards of the color in play.
If you have the same number card of a different color, you can still place your Wild Draw 4.
If a player places a Wild Draw 4 card, another player can challenge them, accusing them of bluffing. If this occurs, one of two things could take place:
If the player does have a card of the color in play: they draw 4 cards and the player for whom the effect was intended must not draw. The game resumes by placing the Wild Draw 4 card at the bottom of the discard pile and the player following the one who had just placed the Wild Draw 4 card can play.
If the player was not bluffing, the card’s effect takes place and the accuser draws 2 cards.
It is possible to place a Draw 2 or Wild Draw 4 card on another Draw 2 or Wild Draw 4 card respectively, but the number of cards to be drawn will not be stacked up and this does not cancel the effect for the player who placed a Draw 2 card.
For example, if player A places a Draw 2 card and player B does the same, players B and C will have to draw 2 cards.
The Uno team has confirmed on Twitter that it is possible to end a game with an action card (Draw 2 or Wild Draw 4, for example) as the screenshot from Twitter proves:
At the start of the game, you can create alternative rules to make the game more challenging:
Make it possible to stack Draw 2 and Wild Draw 4 cards if the player to draw cards has a Draw 2 or Wild Draw 4 card.
Skip the next player’s turn 2 or 4 times in a row, instead of having to draw
Prohibit forcing a player to draw cards because of Draw 2 or Wild Draw 4 cards 2 turns in a row
Allow all players to place their Draw 2 or Wild Draw 4 cards on the first turned over card at the beginning of the game, the player following the one who placed the last Draw 2 or Wild Draw 4 card must draw the cumulative number of cards.
Prohibit ending a game with an action card to make the game more difficult and suspenseful.
Turn Wild Blank cards into Draw 2 and Wild Draw 4 cards.