Before landing, you should see an Anklegator burrowing through the ground, but you can't do anything about it just now. Break through the obstacles in the path to get to a Wallflower and some Peckers. By a campfire along the path is the Sneaky Decoy Secret Skill, allowing the Kid to confuse enemies with a decoy so that he can perform a critical strike. Past this is an adult Pecker that you can test it on. Up the northern path is a sole Pincushion, so take the western path to proceed. The Kid should eventually come across a Stinkweed plant that sends clouds of poisonous clouds in his direction, so destroy it to avoid loss of health and temporarily blurred vision.
Approach the swamp to encounter Queen Anne, a massive Anklegator who has claimed Roathus Lagoon as her territory, and the Brusher's Pike. While this weapon should prove useful in the battle against Queen Anne, it will have many other uses down the line thanks to its strength and reach. Defeat the enemies that spawn and a path will open up. Queen Anne's horn will be visible in the next grassy area, striking from the ground only if the Kid actually steps into the grass. The northern path which leads to the Arsenal is blocked by grass, so if you must access the Arsenal, roll through the grass quickly.
In the next grassy area, defeat the enemies to open the eastern path (the southern path, where the Shard sits, will remain blocked). A northern path here will lead you to a Stinkweed that protects Something Pointy. Progressing through the next grassy area will open up yet another path, but before proceeding, take a branching path off to the side to find a Health Tonic and the Anklegator Egg, a memento that allows you to summon an Anklegator to the Bastion after speaking to Zia about it. Proceed and the Kid will find himself trapped with Queen Anne, though he can also pick up the Shard here. Defeating Queen Anne isn't necessary here, as the Skyway can be accessed in this area after picking up the Shard regardless, but doing so will net the Kid a hefty 840 XP. Dodge over the position of the horn as Queen Anne burrows in the ground to trigger an attack from her, allowing the Kid to strike with the Brusher's Pike (or his ranged weapon of choice). Repeat the process until she progresses in speed and eventually faces defeat.