The Swamp Monster II, originally referred to as the "Mysterious Tentacle Horror" until Ratchet defeated it and thus data was found for it's Monsterpedia entry, was a dangerous creature living in the depths of Oozla, beneath the swamp muck and under the MegaCorp Outlet. It was a large mature female Mutant Swamp Beast, and presumably the mate of the Swamp Monster I that lived around the MegaCorp Outlet. Thus, it was the Mother Beast that gave birth to all of the Mutant Swamp Beasts. The Swamp Monster II was accessible once Ratchet obtained the Gravity Boots.
Living underneath a MegaCorp outpost in a large cavern, this creature was the Mother Beast known to lay the eggs that hatched the Mutant Swamp Beasts. Before Ratchet confronted and defeated it, apparently nobody had seen this mysterious creature and lived; however, Qwark had apparently had a run in with one after his arrival in the Bogon Galaxy and been eaten alive by it. Qwark survived this encounter and escaped, going on to masquerade as Abercrombie Fizzwidget.
It was hidden until confronted by exploring Lombax, Ratchet. Running over the many lily pads around its lair, Ratchet dodged the Swamp Monster as it tried to kill him. It swam through the muck trying to strike Ratchet with its tentacles and claws, pinching its claws wildly, coughing up flying balls of smoky sludge, and chomping down on the Lombax, taking him inside its mouth briefly. After dealing a sufficient amount of damage to the beast, Ratchet killed it and caused it to sink into the muck. With its death, he also obtained the Box Breaker.
Upon regaining his memory aboard the Starship Phoenix in Up Your Arsenal, Qwark recalled being eaten alive by the monster.
- There was a glitch during the boss battle. If a decoy was thrown onto a lilly pad, it would sometimes be invulnerable and the Swamp Monster would not stop trying to hit it until it or the decoy was destroyed.
- Another glitch allows you to face the swamp monster again in Challenge Mode, even if you already have the Box Breaker. Use the decoy glove to walk through the wall and go down the tunnel, and you can battle it again. This can only be done once per game. Trying this glitch again after you defeat it in the same game will result in Ratchet getting stuck halfway down the tunnel.
- This glitch requires you to be in Challenge Mode. Using the First-person mode wall climbing glitch on the wall right next to the huge window in the MegaCorp store, you will go through the ceiling. If you try to go forward once you are above the ceiling, you will fall a little and touch the huge rock on the other side of the window. This will trigger a cutscene, and you will be battling Swamp Monster II. Using this glitch, it's possible to battle it even if you already have the Box Breaker. This also allows you to battle it without the use of Gravity Boots. Using this again in the same game after it's defeated will still get you to Swamp Monster II's place, but the monster will not be there and all the lily pads will be gone, so you will sink into the swamp and die.
- Throwing a decoy right next to the wall beside the big window will cause Swamp Monster II to keep trying to hit it when you actually battle it, if the decoy is still there during the battle. This will allow you to defeat it easily because it will not try to attack Ratchet, only the decoy that is behind the wall. It looks like it is trying to attack the wall because the decoy is on the other side. It will never really damage the decoy, so that it will go on forever until you die or defeat it. When it tries to eat the decoy, nothing will happen and the monster will stop moving. Even though it's trying to get the decoy, it will face Ratchet when it swings it's tentacles or tries to eat the decoy.