The standout addition is the poison dart, which causes enemies to attack one another. This is especially fun during the "Cable News" mission, where you can shoot darts into fire sources to affect multiple enemies at once.
Before you download or back up any save, know where to look. Assassin’s Creed Syndicate uses standard Uplay/Ubisoft Connect save locations.
Because of the dense scripting and physics involved (especially on moving trains), Sequence 4 is prone to save corruption, infinite loading screens, or quest givers failing to spawn.
For most players, the save is ideal. It respects the game’s difficulty curve while skipping the buggiest intro missions of Sequence 4.