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.
in the second cave
He has 800 hp. The second time round he only has about 600.
Porygon Porygon2 PorygonZ Solrock Lunatone Bronzor Bronzong Salamance Metagross Primal dialga (at the summit at your first visit) Dialga (summit if you enter the second time)
Battle him a second time. It is a 100% chance of joining your team.
You can evolve after you beat darkai and get dialga and palkia on your team ( they join after you beat them the second time.)
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.
get a dito from on of the earlier games and leave it in the daycare place with the dialga and they will mate. It helps if you have the daycare app for your pokech. x
Palkia can be recruited olny on the second visit so you will have to go back to where you first battled it then beat it again.Golden Mask is not needed it has a 100% Recruit rate on second visit.
No, you do not get a second chance to catch him in the game you are playing.
Talk to Lapras at the beach, and you can go back to the Hidden Land. Dialga is still at the top of Temporal Tower, though you need to go through all the intervening locations again. However once you defeat him that second time, he'll join automatically.
you can go back and catch: -azelf -Uxie -Mesprit and also a SECOND -Palkia and a SECOND -Dialga
No. In Pokemon Diamond you can only catch Dialga once but you MIGHT have a second chance after beating the Pokemon League at least once.