Anacondas

The Anacondas are gigantic and extremely aggressive snakes, and the titular main antagonists of the film series of the same name.

Description
It is a fictional species of anaconda native of Amazon and Borneo. Due to consuming "blood orchids", a flower that can extend their lifespans, they grow to immense sizes. Therefore, they are much faster, stronger and more agile than normal anacondas. They also have a great intelligence for animals and a highly aggressive behavior.

Anaconda
In the first film, two Amazon Anacondas appear as the main antagonists (along with Paul Serone).

In the waters of the Amazon, an Anaconda attacks a poacher on his boat. Some times later, a television crew arrives in the Amazon to film a documentary and are joined by Paul Serone, a poacher willing to capture an anaconda. After killing a jaguar, the anaconda decides to attack the crew and manages to kill almost everyone, but two survivors finally kill him by shooting him. However, they are later used by Serone to lure another anaconda into a trap. Then, a snake comes but the trap fails and Serone is devoured alive. The anaconda attacks the two others who manage to burn him alive before killing him with an axe.

Anacondas: The Hunt For The Blood Orchid
In the second film, a large colony of Borneo Anacondas serve as the main antagonists (along with Jack Byron).

In Borneo, a native hunter is attacked by Anacondas and is killed. Later, several anacondas assemble into a pit for mating. At the same time, a pharmaceutical researchers team arrives in the area to find "blood orchids". Several snakes attack the team and many members are killed, but Jack Byron, one of the survivors, forces the others to continue the expedition. They find "blood orchids" near the anacondas pit and Jack obliges one of the remaining team members to retrieve some, however things go wrong and Jack falls into the pit where the snakes devour him. The others are then attacked by one of the anacondas but they manage to cause an explosion with a fuel container that kills every anacondas.

Anaconda 3: Offspring
In the third film, the main antagonists are a couple of genetically modified Amazon Anacondas. In this film, they both have spear tails.

The rich industrialist J.D. Murdoch makes capture two Amazon Anacondas in order to experiment on them. However, one day they manage to break out from the lab and go on a rampage. Some mercenaries are sent to recapture the snakes, but many of them are killed. Finally, the anacondas take refuge in an old factory where the female gives birth to several offsprings, but an explosion destroys the building and all of them die, except one.

Anacondas: Trail of Blood
In the fourth film, the last baby Anaconda is the main antagonist. In this film, the snake is able to regenerate.

A surviving Anaconda offspring is captured by Murdoch's men and a scientist makes experiment on him, making him capable of regeneration. However, the snake eventually escapes from his cage and devours him. Murdoch sends some mercenaries but the anaconda devours most of them and also Murdoch himself later on. The anaconda is later blew up by grenades, however he manages to survive thanks to his regenerating ability.

Lake Placid vs. Anaconda
In the crossover fifth film, three Anacondas share the role of main antagonists with the Black Lake Crocodiles.

Sarah Murdoch sends Jim Bickerman and her associate Beach to capture one of the crocodiles from Black Lake in order to create a hybrid with some Anacondas. A crocodile is captured and placed in a laboratory truck, but it manages to break out and frees the three snakes also present on the truck. Later, Sarah sends mercenaries to recapture the reptiles but many of them are killed by the anacondas. The snakes also attack a group of sorority girls and devour some of them, but they are confronted to the crocodiles too. One of the anacondas is killed by sheriff Reba and officer Will Tull while fighting a crocodile, and another is thrown into a helicopter by one of the crocodiles, killing him and the men aboard. The last snake manages to kill several crocodiles but is finally killed by Beach with a grenade.