Big Chomper is the unique first boss for Milla Basset & the first overall boss in Freedom Planet. It is a large green eel found in the last slime pool of Aqua Tunnel with sharp fins along the sides of it's body and a small crest on its head.
Big Chomper has an easily-telegraphed attack pattern; it will spit out bubbles containing bombs (one of which can be picked up by Milla and thrown at the Big Chomper), which Milla can attack to prevent further interruptions during her avoiding of its other attacks. Phantom Blocks works too for speedrunning. It will sink back into the pool, and then leap out, and when it lands back in the pool, the splash it makes will generate small blobs of damaging green slime. Afterwards, it will slowly move back to the back of Milla's raft, and repeat the same pattern. Its weak spot is its open mouth, which Milla will have to attack when it's open in order to damage it. After a few hits, Big Chomper will be defeated, ending the stage.