Defeating Groudon and Rayquaza, separately, as two unevolved Basic Pokémon.
Before all that, your player character ends up having a pretty even battle against Team ACT's own Alakazam. Granted, it's in a cutscene, but that's still pretty impressive.
In this promotional short, it is revealed that Makuhita traveled the world to search for Pokemon to help with training rescue teams. This basically means he went to many dungeons, including Mt. Freeze, to get so much Pokemon.
In DX, if, in a story dungeon that allows Pokemon to join you, you manage to have many Pokemon join you and there is a boss there, the Pokemon that joined you won't hesitate to come in and assist you. This can lead to the Team Meanies boss fight in Sinister Woods becoming a complete joke, considering that you outnumber Team Meanies.
After defeating Rayquaza and it notices the meteor heading toward the planet, it tells you and your partner that the meteor is too close, and that the two of you likely won't escape it destroying the meteor with its Hyper Beam unscathed. Your partner responds that you knew that and that you chose to do this anyway.
Partner: We accepted that from the start!
Rayquaza: Well said! (turns to face the meteor and begins charging a Hyper Beam)
Rayquaza: Take charge of your destiny! (fires the Hyper Beam at the meteor)
The fact that these are the first spin-off titles in the history of Pokémon to ever get a remake.