Dark Rust

"I am destruction incarnate! I am Dark Rust!"

- Dark Rust after defeating Cobalion

Dark Rust is the main antagonist of Pokémon Rumble Blast. It is a Wonder Key that leads the Dark Legion, a an army of rusty Pokémon. It also seeks to destroy all Glowdrops, which heals Pokémon and removes rust from them.

Plot
Dark Rust appears after the player defeats Cobalion. It reveals itself as the leader of the Dark legion when Cobalion's army rusts.

When the player reaches to the deepest level of the World Axle, the player and Cobalion finds Dark Rust below. After defeating many Pokémon and few legendary Pokémon, the player fights many Unown and Sigilyph. Soon, Dark Rust appears and fights the player. The player can't defeat in the first fight against Dark Rust as it has a dark barrier. Cobalion uses its key containing all of its power to destroy Dark Rust's barrier. After the player defeats Dark Rust, it is destroyed as it breaks apart. Due to its destruction, the Glowdrop fountains in Toyland refill again.

It can be rebattled again when the player enters its fort again.

Trivia

 * Like the Bittercold, Dark Rust is a non-Pokémon villain who are the final bosses of the games they are at.
 * While it is not a Pokémon, it has its own cry.