my post from the other topic that asks about how to recruit legendarys
these are the factors that determine whether the legendary pokemon is going to join your team or not:
1)your leading pokemon's level must be higher than the legendary you want to recruit
2)Some legendarys require a certain rank so they could join your team..... "some"
3)body size, most legendary pokemon's body size are 4 stars so have one pokemon that has a body size of 2 stars OR two pokemons that have a TOTAL body size of 2 stars before battling the legendary pokemon
4)Team Size (in other words, total pokemon that walk along in a dungeon) - maximum team size is 4 pokemon
5)Friend Areas *NOTE that some legendarys will automatically give you their freind area after they join you*
6)*OPTIONAL* The "Friend Ribbon", which lets you have a higher chance of recruiting pokemon
7)luck
8) The team leader must be the one who beats the legendary pokemon