A new software update is available for download with many updates including the new Clam Blitz game mode. You will be able to start playing after the update is released on December 12.
In Clam Blitz, competing Inklings are tasked with collecting clams scattered around the stage. After one is picked up, the clam follows the player. The objective is to throw the clam into the basket near the opponent's base. The first team to score 100 points wins! But, of course, this being the fiercely competitive world of Splatoon 2, things are not as easy as they seem. The baskets are protected by a barrier, which much be destroyed first. After collecting 10 clams, the player will earn a Power Clam. These super-powered clams are the key to breaking the barrier, so strategy will definitely be involved in which clams are used to destroy the barrier and which are used to earn points. Not to mention the extra-satisfying opportunity to steal opponents' clams by splatting them.
For complete notes on what is being added and instructions on how to download the update, visit the official Nintendo customer support site.