The Intruder

The Intruder, also known as the Mutant Fish, or simply the Alien Fish, is the main antagonist from the Feeding Frenzy Universe. Specifically, Feeding Frenzy 2: Shipwreck Showdown. It's never revealed how it arrived on Earth, but it was studied by humankind for a while and managed to escape, unable to be contained and controlled.

Appearance
The Intruder, despite mostly being compared to an anglerfish, holds a physical anatomy more similar to whales or dolphins. Its skin has a greenish hue with a prominent, bony lower jaw. Its frontal fins are fairly longer than most fish, and it has a rather prominent "lure" protruding from its head and trailing behind it.

The Intruder is, according to the franchise its from, the largest known predatory fish in existence, outsizing even the prehistoric Megalodon by an extra twenty feet. However, throughout the game upon every defeat, it becomes smaller and smaller, ending up at only four feet by the end.

Behavior
The Intruder shows little to no signs of fear towards other sea creatures, and Humans. It also has a habit of wrecking passing ships, making it a slowly growing threat to humanity.

Abilities
The Intruder is an extremely large fish, and therefore very durable. It is able to withstand most, if not all, naturally known defense mechanisms (venomous attacks, electricity, etc.), and its skin is durable enough to handle even the explosion of sea mines.

While not explained how, it is also capable of changing the temperature of the water on a global scale. This indicates that its homeworld waters are naturally warmer than those on Earth.