1. Raises the power of Rock-type moves by 20%: This means that any Rock-type move used by a Pokemon holding the King's Rock will be significantly stronger.
2. Increases the chance of a critical hit: The King's Rock has a 60% chance of causing a critical hit on a Pokemon, making it a powerful tool for inflicting massive damage.
However, the King's Rock is not a held item in the anime series. It's only used by the Pokemon Kingdra in the episode "A King's Problem" to evolve from Seadra.
So, in Pokemon Indigo, the King's Rock primarily serves as a key item for evolution, rather than a held item with in-battle effects.