What happens when you get regice regirock and registeel in blue rescue team?

In Pokémon Rescue Team Blue, when you obtain Regice, Regirock, and Registeel, you unlock a special event that allows you to access the Underground Ruins. After recruiting all three Legendary golems, you can also encounter and recruit the Legendary Pokémon Regigigas, which is located in the same area. Collecting these Pokémon adds to your team and enhances your gameplay experience.