On several occasions you'll be required to navigate a giant 8-ball around some seriously precarious platforms. This might mean tackling a room with a limited supply of ink, so every single shot has to count. Each one forces you to rethink practically everything you know about the series, and adapt rapidly to some seriously difficult tasks. The challenge rooms themselves are, quite possibly, a new high point for Splatoon 2. You'd have to seriously screw up a lot in the early stages to be unable to continue on, and you can always return to earlier levels with cheaper entries to build up your points again. These points are required to play each of the levels, but they're in plentiful supply. Upon entering a level, you're usually given a choice of equipment to play with - all levels can be completed with each setup, but using ones less suitable for the task grants you additional points upon completion. Complete one and you unlock its neighbours, sometimes opening up entirely new lines to explore.
You get around via a subway map, which is made up of a series of challenge rooms. The Octo Expansion sees you taking control of Agent 8, an amnesiac Octoling tasked with collecting four "thangs" from around a strange facility in order to escape to the surface. It also offers up incredibly tight level design, tough battles you'll never forget, and one of the best experiences you'll have with Splatoon 2 by far.