This mod is simply from Pokémon Mystery Dungeon: Explorers of Sky, which I would call Pokémon Mystery Dungeon: Legendary Edition, which is a simple change from starter Pokémon, in that case the cover shows Mew, Celebi and Jirachi as the three notable Pokémon ...
That's why that means when you do the Pokémon Test you want to be:
You have 40% of it being Mew.
30% of you being Jirachi.
15% of you being Celebi.
5% of you being Pikachu, Jigglypuff, and Charmander.
You have 75% of you being Celebi:
35% pink (shiny).
20% for you to be Mew or Jirachi.
5% for you to be Jigglypuff, Eevee, and Pikachu.
Once you have selected your hero Pokémon, now it is your turn to select your partner, in that case most of them are legendary such as:
Mew (repeated), Mewtwo, Jirachi (repeated), Zapdos, Rayquaza, Manaphy, Celebi (Both repeated), Pikachu (repeated), Jigglypuff (repeated), Moltres, Articuno, Lugia, Suicune, Ho-Oh, Entei, Raikou, etc (that I don't remember anymore ...) those Pokémon are the ones you will choose to be your companion throughout your adventure.
This game was modified thanks to a user called Evandixon whose program is: Sky Editor: Rom Editor.