These are the rules tables argue about most. Agree on them before you start; you can turn them on or off when you set up the game.
Draw Two on Draw Two (stacking)
When a Draw Two is played on you, you can play your own Draw Two instead of drawing; the next player then draws 4, and so on.
Draw Two on Wild Draw Four, and the other way round
A Draw Two can be answered with a Wild Draw Four and the other way round; the cards to draw add up.
Wild Draw Four can be challenged
A Wild Draw Four may only be played when you have no card of the current colour. The next player can challenge: if you broke the rule you draw 4, if not they draw 6.
7-0 rule: a 7 swaps hands, a 0 passes all hands on
Whoever plays a 7 swaps hands with a player of their choice. When a 0 is played, everyone passes their hand to the next player in the direction of play.
Jump-in: play an identical card out of turn
If you hold exactly the card just played (same number and colour), you can play it straight away, even when it isn’t your turn; play goes on from you.
A drawn card that fits must be played
If the card you draw can be played, you have to play it at once instead of keeping it.
Keep drawing until you can play
If you can’t play, you keep drawing until you get a card you can play, instead of drawing just one.
No going out on an action card
Your last card can’t be an action card or a wild (Draw Two, Reverse, Skip, Wild, Wild Draw Four); you have to go out on a number card.