A returning feature to the Pokéon Rumble series, last seen in Pokémon Rumble Blast, are Rusty Pokémon. After you reach Rank 50, you will start picking up the occasional Rusty Pokémon. These Pokémon are denoted by a crimson name and ability stating that they are Rusty.
When in battle, these Rusty Pokémon only have the ability to use the move Struggle, making them next to useless, however there is a way to heal them. If you get to Rank 58, you will get a challenge by the king where, if completed, will give you the Rust Removal Spot to be put in your town.
|Cleaning Rusty Pokémon|
When you go to the Rust Removal Spot with a Rusty Pokémon, then you will get the option to clean it. This will cost 1 Poké Diamond per Pokémon, though the first one is free. Select the Pokémon you wish to clean and exit out, and then it will be clean.
These Pokémon are worth cleaning, however. They often have good traits, often blue ones to get multiple traits, as well as powerful moves.