List of post-release content in Splatoon

Downloadable Content, or DLC, is content that will still be in development at the game's launch, but will be released periodically as more is completed. Nintendo of America's official Twitter has stated that "Every week or two, new free content will be introduced in #Splatoon, including weapons, stages and gear."

N-Zap '85
The N-Zap '85 is a shooter-type weapon released on June 1st, 2015. It is very similar in stats to the Splattershot Jr., but lacks its range. It's sub weapon is the Splat Bombs, and it's special weapon is the Echolocator. To unlock this weapon, one must reach level 5, and pay 3,500 coins.

Port Mackerel
Port Mackerel is a stage released on June 1st, 2015. Like majority of the other maps, it is symmetrical, and like Kelp Dome it has multiple isles.

Ranked Battle
Ranked Battle is a mode that was released on June 1st, 2015. It allow two teams to fight for control of predetermined locations on a stage.

Inkbrush
The Inkbrush is a Roller type weapon, and will have a far thinner coverage than its Splat Roller and Dynamo Roller siblings, but will allow the player to move significantly faster. It was shown off in the Splatoon Nintendo Direct on May 7th, where it is showed off in action

Tower Control
Tower Control is a Capture the Flag Style game mode that will be released post launch, presumably before August.

Rainmaker
Virtually nothing has been revealed of this mode other than its name. During the Nintendo Direct where the mode was announced, the following picture was released, however.

HUGE POST-LAUNCH UPDATE EVENT
This August, a "huge matchmaking update" is expected. This will add a slew of new matchmaking features, including friend-based matchmaking. This will allow either 4 NNID friends to team up against another group of 4 NNID friends, or allow 8 NNID friends to secure a lobby for themselves, where the group will be able to decide the stage and ruleset.