Buddy

Players can ask to be someone's friend by clicking on the other penguin, then clicking on the smiling face on the bottom left of their player card. Say "yes" if you wish to ask to be their friend, say "no" if you have made a mistake or have decided not to be their friend. An envelope appears when they have answered your request.

The penguin you asked can say "yes" or "no" to you asking to be their friend. If an envelope dosent appear straight after you have asked them, then their friend list is most likely full.

On Rockhopper's player card, there is no add friend button, instead there is a button to get a free Rockhopper backround.