Slattern is the first and only known Category V Kaiju ever encountered by humanity.
The largest and strongest of all the known Kaiju, Slattern is unrivaled by any of its brethren in battle. The creature's high toxicity levels and intelligence makes it the most lethal Kaiju the Pan Pacific Defense Corps has ever faced.
Slattern has thick, leathery skin and three triple-crowned tails that can be used for long distance attacks or piercing the armor of a Jaeger. Its tails have enough power to rapidly spin and lash out, acting as a mid-range attack, even with a heavy amount of underwater pressure working against them.
It also has a spike-like protrusion on its chest, which can extend forward and inflict blunt damage on a Jaeger. The sound of Slattern's roar can emit sound waves that cause visible damage to the environment it is situated in. Slattern's body is extremely resilient against attacks and its impressive size strikes fear into its foes. Slattern's height is estimated at 596 feet and its weight is estimated at 6,750 tons.
Slattern's face is rather unique, with a symmetrical facial structure similar to a hammerhead shark that contains two blue eyes on each side. The Kaiju's chin is slanted. Like Scunner, Trespasser, and Knifehead, its arms are actually fused, ending in three-digit claws.
When the Precursors learn of Operation Pitfall, the Defense Corps plan to destroy the Breach, through Newton's Drifts, they send Slattern and two Category IV Kaiju, Raiju and Scunner, through the Breach to protect it.
Slattern emerges from the Breach just after Gipsy Danger and Striker Eureka arrive to destroy it. It attacks Striker Eureka with its tails, sending it crashing into a hydrothermal vent, damaging the Jaeger severely. Raiju and Scunner cripple Gipsy Danger, preventing it from assisting the downed Jaeger.
As Striker Eureka recovers from the first attack, Slattern tackles the Jaeger and uses its environment to cause further damage. Despite being three times larger than Striker Eureka, Slattern is still met with considerable resistance. Striker Eureka cuts Slattern's throat and nearly amputates both its front arms with its Sting Blades.
When Slattern realizes it's losing, it calls for aid. Scunner answers the call for help, abandoning its fight with Gipsy Danger as Slattern retreats to safe distance. Once Scunner arrives, both it and Slattern charge Striker Eureka as the thermonuclear bomb is detonated by its pilots. The blast kills Scunner, but Slattern survives, severely wounded.
Slattern intercepts Gipsy Danger's attempt to enter the Breach with the severed half of Raiju. With no way around Slattern, Gipsy drops the half of Raiju's carcass and tackles Slattern, sending them careening over edge toward the Breach. Slattern uses its tails to disable Gipsy Danger, stabbing it in the back. It ruptures one of the pilots' air supplies. As the Kaiju and the Jaeger approach the Breach, Gipsy Danger fires its nuclear turbine.
The resulting blast burns through Slattern's chest and its internal organs, killing it. Slattern's body is used to bypass the Breach and enter the Anteverse, allowing Gipsy Danger to destroy it.
- Guillermo del Toro likened the Slattern to the Devil and the character Chernabog from Walt Disney's Fantasia short, Night on Bald Mountain.
- Slattern is playable DLC character Pacific Rim: The Video Game.
- "Slattern" is a term that dates back to the seventeenth century. It refers to a sexually promiscuous or dirty and untidy woman.
- In the novelization of the film, Stacker Pentecost names the Kaiju "Slattern" after Tendo Choi calls it a "big bitch".