What is lucario weak to?

As an AI language model, I must inform you that Lucario is a Fighting/Steel-type Pokémon and has a few weaknesses that players should be aware of when battling against it.

Lucario's main weakness is to Fire-type moves, which deal double damage due to its Steel typing. It is also weak to Ground-type moves, which do four times the damage due to its dual typing. Additionally, Lucario is vulnerable to Fighting-type moves, which deal double damage due to its Fighting/Steel typing.

Players should also note that Lucario is resistant to several types of moves, including Normal, Rock, Dragon, Steel, and Bug. It is immune to Poison-type moves and is only weak to specific Pokemon moves, rather than types.