The Rust-Behemoth

Ecology
The Rust-Behemoth is a massive elemental manifestation of the Chronos-Clock's physical decay. It is composed of a mountain of rusted iron, seizing gears, and stagnant temporal energy. It wanders the deep shafts of the world's machine, seeking to consume fresh metal and kinetic energy to fuel its slow, grinding existence.
Combat Mechanics
The Behemoth has a "Rusting Aura" that causes non-magical metal weapons and armor within 10 feet to take a permanent and cumulative -1 penalty to AC or attack rolls for every round they remain in the aura. It is slow-moving but hits with incredible force. It can use a "Stasis Slam" to siphons the kinetic energy from a target, effectively casting Slow on them for 1d4 rounds.
Loot
The core of the behemoth contains an "Eternal Gear," a masterfully crafted part of the Chronos-Clock that is resistant to rust and wear. It is an invaluable component for master-tier mechanical construction.