The Battle at Kemble's Cascade: Cetus features a huge Lovecraftian eel that serves as an intermediary boss level during the game.
Cetus appears following the asteroid stage and sits at the top of the screen (as a temporary sixth row) while the wormhole stage scrolls normally below it.
At the beginning of each round, Cetus draws from its own "boss" sector card deck, revealing either a wormhole or a burst bomb. To determine which column receives this payload, draw from the regular sector card deck and match its special icon to the corresponding boss segment.
Cetus sticks around long enough to dump two bombs and two wormholes onto the star field, then it takes off. This beast is worth a fair number of points and bellonium, but its head and belly are immune to Gamma, so you need alternative methods to take those out.