Splatoon 2 isn't just a remake of Nintendo's most popular shooter. They're adding a lot to the game where you mark your territory by shooting your ink all over a map and your opponents. One of those additions is a new co-op mode where players work together against a common enemy, the salmon.
Splatoon 2's new mode is called Salmon Run. This mode pits four players on a map with the goal of overcoming wave after wave of enemies. These enemies get progressively more difficult and shoot a sickly green ink of their own. The true goal isn't just to stay alive, it is to collect special golden eggs. These eggs can only be obtained by defeating boss salmon like the steelhead.
Not only is this new mode a way for players to work together against nonhuman enemies, but it will have special rewards you can only get by playing Salmon Run. Instead of respawning when you are downed by an enemy, you'll pop out a little life preserver and wait to be rescued. How are you rescued? Why by having a teammate shoot you with some ink of course.