After you have defeated the Elite Four and champion head to Eterna City and go to the house on the southwest corner. There you will see Professor Oak and he will tell you that the three legendary birds have been spotted roaming Sinnoh. You have as many chances as you want to catch the legendary birds. Just make sure you have mean look shadow tag or any trapping ability or move. Good luck!
yes
152 is rotom.
An event
you can't
You can't, you have to Migrate him over or trade.
You can't catch Mewtwo in-game in Pokemon Diamond.
You can't get Articuno in Pokemon Ranger.
It is impossable to get one in Pokemon diamond,but there might be one in Pokemon platinom...... hope that helped!
articuno is not in pokemon world 7.6
Golbat uses mean look in Pokemon pearl but i am not sure about Pokemon diamond and pearl.
No trainers will have articuno.
Barboach. You can get it in the Safari Zone/ Great Marsh.