This feature (enabled for paying members only) masks your last action which is displayed next to your name when you are online. It means that if you activate the cloak mode on the Settings page, nobody can see which BrainKing page you are currently viewing.
(hide) If you want to play a game with an opponent of a similar level, you can define a required BKR range for a new game invitation. Then nobody with a BKR outside this range will be able to see/accept it. (Katechka) (show all tips)