When first entering Area 4, Propeller-Lift Fortress can be found under the area. Fall down the large gap you see—there should be two Inkrails and a Gusher. Take the Inkrail on the left. A Gusher and extra platforming can be found. Propeller-Lift Fortress can be found at the end.
The very first section of this mission holds two Propeller-Lifts. It holds four Octotroopers and one Armor to collect. There is an Inkrail to use to advance toward Checkpoint 1.
After using the Inkrail, there is another Propeller-Lift that can raise several platforms, along with three Octoballs and an armor to collect. Agent 3 can advance to Checkpoint 2 with or without raising the platforms with the Propeller-Lift.
The first part of Checkpoint 2 holds three Octobombers and an armor to collect. There is a Propeller-Lift located above the Octobombers. It's best to splat them so they won't distract Agent 3. After passing that is an area similar to Checkpoint 1, but there are there Octotroopers. The Armor is located on one of the platforms which needs to be triggered to raise the Propeller-Lift. To advance to the next Checkpoint, the player will have to use the Propeller-Lift to elevate them to the launchpad, heading to Checkpoint 3.
After taking the launchpad, Agent 3 will be put in an area surrounded by water. There is a Propeller-Lift in the distance and can only be reached with the Ink Cannon after shooting the Propeller-Life with the Ink Cannon, but there is a single Octocopter guarding the Ink Cannon. A platform will reveal when Agent 3 successfully hits the Propeller-Life with the Ink Cannon. Take the Platform to get across the water. The player will meet five Octocopters and an Octobomber that awaits near the end of the ride. There is a Launchpad after climbing the wall, leading to the final Checkpoint.
Once Agent 3 has reached the final checkpoint, there will be two Propeller-Lifts, one with a bubbler on it. Once they've jumped off the platform, an Elite Octoling will appear. Splat it then another one will appear. Once you've splatted both of them, a launchpad will appear. Super Jump to the platform with the Zapfish then burst its shield.