Bronzong

You know, Bronzong is perhaps the only Pokémon there is without any weaknesses. All attacks are either just normal damage or not very effective on it, and a couple don't work on it at all.

Like, almost all of its type weaknesses are cancelled out by its other type, such as its Fighting Weakness from Steel is nullified by Psychic, and its Ghost weakness from Psychic is nullified by Steel.
Plus, it's two special abilities cover the two weaknesses that it's types don't cover. It's Heatproof Ability makes it no longer weak to fire, and its Levitate ability makes it no longer weak to Ground.

No other Pokémon has no weaknesses like that. That's what makes it so awesome!