On some of the games I notice a number and a smiley face. What is it for?

According to their website, “ Ever wonder why an emoji appears on your game list?

From now on, you will start seeing emojis on your game list, particularly on games which you've been playing with the same person for at least 3 consecutive days.

In addition, you will also see a number beside the emoji. This represents the playing Streak that you and your friend have established. If you break the Streak, the emoji disappears until both of you establish another playing Streak for 3 consecutive days.

The emoji gets cooler with every day added to your Streak.”