you have to battle with lv 25 Pokemon
get a reviver seed, train good and use thunder shock on articuno. or thunder bolt
you defeat them and some will join
you can evolve your starter pokemon
Simply defeat it in Frosty Forest after beating the game, and with a little luck-you may have to try several times- it will ask to join your team.
Defeat them while you're in their dungeon.
defeat darkrai mission
Defeat a lot of Pokemon.
First, Recruit an Articuno. Second, Teach it Powder Snow. Third, Level Articuno up to around Lv. 80-100. Fourth, Defeat a Monster House with it. you should defeat all opponents in one turn and earn a massive EXP. boost. *If Articuno is not available at the time teach any Pokemon Vacuum-Cut.*
Just keep Attacking till it is defeted.
Link box and plenty of reviver seeds!
Yes, all legendary pokemon will reappear if you defeat them and fail to recruit them.
only if yhe legend on your team is small like entei can recruit suicune i think