Nintendo recently announced what the upcoming paid DLC packs for Splatoon 3 are. The DLC is coming in at least two “waves”, or packs. Both of these waves are available for purchase from the eShop, though players will still have to wait for the packs to release. A single purchase of USD 24.99 / EUR 22.49 will give you access to both waves once they are released.
Wave one allows players to explore the original Splatoon’s Inkopolis lobby, with a couple of changes. It now includes a building for Salmon Run and an area for Table Turf, a couple of shopkeepers have been replaced accordingly, visual upgrades, and updated designs. For example, two smaller horseshoe crabs, Shelly and Donny, replace Sheldon in the weapons shop. The Squid Sisters return, performing during Splatfests and are visible in their studio as they were in Splatoon. The train station next to the Splatsville battle lobby will be where players access Inkopolis.
Also announced was wave two, called “Side Order”. It launches sometime in the future along with wave one, and seems to be an additional singleplayer campaign. While relatively little is shown, it seems to be based on the “Order” prompt from the final Splatoon 2 Splatfest. Shown off in the trailer are Off the Hook from Splatoon 2, hinting at their involvement. Otherwise, info on Side Order is sparse, as the trailer showed off very little of the DLC.
Source: Nintendo Direct 2.8.2023