How do you get the guard out of way in mount coronet at top Pokemon diamond?

In Pokémon Diamond, after defeating Team Galactic and acquiring the Master Ball, you will gain access to the top floor of Mount Coronet. There, you will encounter the guard who blocks the path to Spear Pillar, the final area in the game.

To get the guard out of the way, you must first speak to him. He will refuse to move unless he witnesses the power of legendary Pokemon like Azelf or Dialga that resides in Spear Pillar.

At this point, you must have already captured Pokemon at the Lake of Valor, Lake Verity, and Lake Acuity. Now, proceed back to Spear Pillar. Upon entering the area, you will encounter a legendary Pokemon who will unleash its power.

After the legendary Pokemon shows its extraordinary abilities, the guard will finally recognize your strength. He will step aside, allowing you to pass through to Spear Pillar and challenge the final boss of the game.