holy stuff this is one good holiday update
https://twitter.com/i/moments/932976630791798784new hairstyles, 140 gear items, 5 new stages (2 returning from the original game, 1 stage in salmon run), new music, and a new ranked mode involving clams you have to collect and throw into the enemy's basket
edit: full list (source
https://www.reddit.com/r/splatoon/comments/7ei0nk/new_hairstyles_hydra_squeezer_weapon_type_and_more/?limit=500)
New Map: MakoMart coming this Saturday.
New Map: Shellendorf Institute
Returning Old Maps: 'Walleye Warehouse' and 'Arowana Mall'
New Salmon Run Stage 'Salmonid Smokeyard' coming this Friday.
New Ranked Gamemode: Clam Blitz coming mid-December
140 New Pieces of Gear coming this Friday
New Hairstyles, 2 male, 3 female in screenshots, trailer shows more
Posing with Amiibo at pre-set locations in Battle Stages to take photos
Gear can be swapped in the match room
Level cap raised to 99, you then have the option to start over at 'Level ★1'!
New Weapon: Squeezer
New Weapon: Glooga Dualies
Another new weapon being a see-through Brella
New weapon: Hydra Splatling
New Battle Tunes by 2 new bands