Seems like a no-brainer.
Will increase forum community membership from players playing on kong that do not know the forums exist and can improve new player retention rate by giving them easy access to a community of people who love the game and are willing to help them.
Just make sure it opens in a new window.
The ability to add players as a friend in game would be fun. Just putting it out there.
Also when you beat a player in pvp, make it so that it shows there name and gives a timestamp. Would help for pvp events where you might not have taken a screenshot before win screen.
If marks and nymphs are going to be in the game, only/winable from pvp forum events, please make it so that upgrading either of these doesnt cost you anything in terms of useability in said pvp events. (Aka having upped nymphs unuseable in unupped events)
While I'm here I might as well add that making upgraded marks stack with your in game mark of the same element would be great. Main benefit of marks is that they stack unupped, shouldnt remove this advantage by upgrading them.
Ranty, but just some thoughts atm.