Of course there are always different variations of house rules, but there is just one set of rules which can be called the true and correct UNO rules. It is said, that even the ancient pharaohs were in disagreement about certain cases. The following statements and quotes are directly taken from the official rulebook, which can be found here (last visited 06.12.2020).
Stacking 2+ and 4+ – not possible
- 2+ :“When you play this card, the next person to play must draw 2 cards and forfeit his/her turn”
- 4+: “[…] requires the next player to pick 4 cards from the DRAW pile and forfeit his/her turn”
So NO stacking 2+ and 4+ whatsoever. Also confirmed by twitter posts, see hypebeast.com.
Ending with an action card – possible
There is nothing stated in the original rules, that you can not end the game with an action card, which includes a 2+ or even a 4+ card. Also confirmed by twitter posts, see mashable.com.
Not saying UNO – 2/4 cards penalty
- “Before playing your next to last card, you must say “UNO”. […] If you don’t say UNO and another player catches you with just one card before the next player begins their turn you must pick FOUR more cards from DRAW pile.”
- “If you forget to say “UNO” before your card touches the DISCARD pile, but you “catch” yourself before any other player catches you, you are safe and not subject to the 4 card penalty”
As soon as you take the second to last card from your hand and initiate your playing motion you should call out UNO. If you played your card, you effectively have only one card left, and other players can then call you out. Furthermore the penalty is to pick FOUR more cards. Although the amount of cards to be drawn are widely inconsistent even within Mattel’s own official rulebook. For comparison see this, where the penalty is only drawing 2 cards.
Mysteries about 4+ – only playable if nothing else possible
“However there is a hitch! You can only play this card when you don’t have a card in your hand that matches the color of the card previously played.[…] A Player may play a “Wild Draw Four” card even if they have a matching number or word card of a different color in their hand. If you suspect that a player has played a Wild Draw 4 card illegally, you may challenge them. A challenged player must shot his/her hand to the player who challenged. If the challenged player is guilty, he/she must draw the 4 cards. If the challenged player is not guilty, the challenger must draw the 4 cards, plus 2 additional cards. Only the person required to draw the 4 cards can make the challenge.”
You can only play the 4+ card, if you are not able to play any other card. If you do so regardless having another playable card, the player who hast to draw the cards can challenge you which let’s him see your hand. If he is right you draw 4 cards, if he is wrong he draws 6 cards instead.
Drawing a card and play immediately
“If you don’t have anything that matches, you must pick a card, from the DRAW pile. If you draw a card you can play, play it.”
UNO reverse – acts like a skip card in a game with 2 players
“Playing a Reverse card works like playing a Skip card. By playing the Reverse card, you may immediately play another card”
The original UNO rules state, that as soon as one player wins the game, points are calculated, but we all know, noone actually does that. Instead it’s a deathmach until the last 2 players are left. Here the rules for 2 players come into play. So reverse acts like skip.