Unwelcome Flying Object is the twenty-first mission available in singleplayer Octo Valley. It takes place in a modified version of Urchin Underpass, a multiplayer stage.
Mission 21 can be found on the Tower further away from the entry of Area 4. There are 2 ways of getting to Mission 21:
Option 1: Head to the tower on the right, there should be a geyser underneath the tower and an Inkrail when taken the Gusher. Activate it and fall down the hole. Agent 3 will be placed to where mission 19 is located, and there is a Propeller-Lift to take. Use the Propeller-lift and it'll take Agent 3 to a long cube platform with an Inkrail installed. Use the Inkrail and it'll take Agent 3 above Mission 21. Clip through the grate in squid form and Agent 3 will find the kettle to Mission 21.
Option 2: There is a shortcut to take underneath Area #4, when close to Mission 16, Perform a Swimming Squid Jump to the long Cube platform. Use the Inkrail on the Cube and it'll place Agent 3 above mission 21. Slip through the grate in Squid form and Agent 3 will find mission 21.
Starting off Mission 21, Agent 3 is put in Urchin Underpass. There are filled crates, one of the crates holds armor. There is an Octocopter hiding behind the crates. Not jumping off, there are Octotroopers to the left and right. Other Routes are blocked off, so just continue on the mission.
Checkpoint 2
Off Course: If Agent 3 goes into the ally of the map, there are 2 large empty crates. Breaking them will reveal 2 Octoballs. There are also 2 small crates that hold a lot of Power Eggs.
On Course: An Octocopter is guarding the entry to the central part of the stage, but that's not it. There can 3 Octotroopers and 2 more Octocopters guarding the other side. There is an Inkzooka there to fight them off. After they are taken care of, head to the next checkpoint.
Checkpoint 3
There are now 2 Octotroopers guarding Agent 3's way through the grate, but there is a sponge that can be used for a shortcut or for hiding from the Octotroopers, but Hiding from them won't be the exact answer since there is an Octostriker watching your every move. As you get past the 2x Octotroopers, now getting up to continue the mission, there are 2 more Octotroopers to fight. Once they've been taken care of, There is another sponge to use. A Bomb Rush Special is at the height of the sponge, which the Bomb rush used Burst Bombs. Agent 3 will also face off 2 Octobombers, using the Bomb Rush will make it a small fight easy. Now Onto the UFO Hideout!
UFO Hideout
Agent 3 is now against the Octostriker. The Octostriker hires Octotroopers to try to keep Agent 3 away. There is an Inkrail installed if Agent 3 doesn't wanna go up above the small wall where the Octotroopers spawn. There is a way to make this fight extremely easy. If Agent 3 saves the Inkzooka from Checkpoint 2, The Inkzooka will do a ton of damage to the Octostriker. The same goes with the Bomb Rush special, but make sure it always hits the Octostriker. After the Octostriker's defeat, the Zapfish is all in Agent 3's hands.
What is this? It looks like the proprietor of that shoe shop! Could there have been an ancient creature that consumed prawns as food?! A terrifying thought indeed...
Location: At the Northeastern part of the map at the end of a side path. Go through the level normally until you reach the checkpoint just after the central area of the map. Take a right through the wired fence and continue down that path. Defeat the Octarian along it and grab the scroll.
swimming to zip out of the way of the Inkstrikes!
-then toss out as many bombs as you can!
