When you fight him the first time, he is unrecruitable. When you fight him the second time, his recruit rate is 100%, ie, he will automatically join.
no you cant =(
u Can Recruit arceus,shaymin,dialga,palkia, and giratina
u recruit palkia and dialga
after u have defeated primal dialga go and defeat him again and he should ask to join your team
You can't get Dialga in the start of the game! You can recruit Dialga after the 20 capters in the 2nd story.
He's in the same place you left him, at the top of Temporal Tower. Go to the beach to speak to Lapras to take you back to the Hidden Land. You have to navigate through all the same levels as you did during the first time you came, but Dialga's recruit rate is 100% at least.
NO ONLY ONCE...VERONICA
If you mean Explorers of Time/Darkness, go to Temporal Tower, beat Dialga. Then go back and fight it again. Beat it. And tell it to join you. Well yeah pretty much what he said but I would just like to add one thing: No matter what-even if you have the worst luck ever-Dialga will join your team since it is one of those Pokemon that have a 100% recruit rate Have Fun! ;P
Dialga is easier to catch Palkia is a bit tougher to catch but Pokemon level 75 will do the trick.
You can't recruit Pokemon from the Hidden Land or Temperol Tower.Sorry.
You can recruit Celebi by going to Mystifying Forest at floor10. You will need to bring a mystery part or secret stoneplate.( To get items, google the sentence " mystery dungeon wondermail generator", the website is upokecenter. To improve your rate of recruiting you need a friend bow.I jope this helps. Go Pokemon!!
First you have to defeat primal dialga to save the world and to continue the story. later after the credits roll, if you want to recruit dialga, you can battle him.