Fight other people in real time. Quick Match drops you into an open arena. Or make a private room and send the code to friends. Up to 8 players, first to 15 eliminations.
Map for private rooms is the one picked on the Maps tab. Quick match rooms use the map of the room you land in. Multiplayer needs a network connection to Firebase, which works when the game is opened from its own page.
There are hidden things in every map, plus a few secret codes. Nothing tells you where. Found secrets are saved to your account, and each one pays 30 Bottlecaps.