Like in previous games, you can make legendary pokemon your companions too, but naturally, it will be harder than the average wild pokemon, though the conditions still base on the following factors:

1) Your leading pokemon's level
2) You rank - this is especially so for certain pokemon, which is known not to join you until you have at least the Platinum or Diamond Rank, so being in the Rukario Rank is always the safest bet
3) Presence of Friend Area - not needed for some legendaries
4) Team size
5) Body size - especially important as most legendaries are of body size 4
6) The Friend Ribbon
7) Who beats the wild pokemon
8) Luck


Pic: Name: Size: Level: Location: Requirements:
Articuno 4 53 Frozen Trees Forest - Forest Center 5/F Only after credits roll
Zapdos 4 45 Thundercrash Mountain - Mountain Top 3/F Only after credits roll
Moltres 4 52 Fire Mountain Mountain Top 3/F Only after credits roll
Mewtwo 1 40 Western Cave 99/F Must have Friend Area Enigma Cave
Mew 1 40 Underground Ruins 36/F onwards Must have Orgel in item bag
Raikou 1 45 Lightning Great Land 30/F Only second visit onwards, must have Friend Area Sacred Great Land
Entei 1 45 Fire Great Land 30/F Only second visit onwards, must have Friend Area Sacred Great Land
Suicune 1 45 NorthWind Great Land 30/F Only second visit onwards, must have Friend Area Sacred Great Land
Lugia 4 30 Silver Sea Inlet 99/F Must have Friend Area Deep Sea Current
Ho-oh 4 50 Far-off Mountain Top 40/F Must have Friend Area Rainbow Peak
Celebi 1 45 Pure Forest 99/F Befriends without need of battle, must have Friend Area Healing Forest
Regirock 1 18 Underground Ruins 15/F Must have Friend Area Prehistoric Ruins, having the item Rock Parts helps
Regice 1 23 Underground Ruins 25/F Must have Friend Area Prehistoric Ruins, having the item Ice Parts helps
Registeel 1 25 Underground Ruins 35/F Must have Friend Area Prehistoric Ruins, having the item Steel Parts helps
Latias 1 28 Fallen Valley 25/F Automatically befriends after saving it, must have Friend Area Southern Island
Latios 1 30 Northern Mountain Humps 25/F Automatically befriends after saving Latias, must have Friend Area Southern Island
Kyogre 4 25 Stormy Sea Regions 40/F  
Groudon 4 37 Magma Underground - Deepest Grounds 3/F Only after credits roll
Rayquaza 4 45 Sky Tower - Tower Top 9/F Only after credits roll
Jirachi 1 40 Wish Cave 99/F Must have Friend Area Moon Gaze Mountain
Deoxys 1 35 Meteor Cave 20/F  

 
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