Via Tom Henderson:
The new co-op game mode, codenamed LEAGUE, is under development at Ubisoft but doesn’t have a set release date due to the game’s recent postponement, which is affecting the entire Assassin’s Creed pipeline. However, sources tell me that LEAGUE was in development long before the postponement and that this wasn’t an addition because of the delay.
While specific details on what the game mode actually entails are slim, presumably, the co-op mode will see Naoe and Yasuke fight side-by-side, using their different combat abilities to take out enemies.
EXCLUSIVE - Assassin's Creed Shadows Co-Op Mode Is in Development
Assassin's Creed Shadows currently has a co-op mode in development, which is scheduled to release post-launch.
insider-gaming.com