Mt. Silver
you either get it on the peak area on the safari zone or you go into mount silver cave
You can't
you can't
safari zone
You need to evolve Lavitar to get a Pupitar at level 30 in Pokemon Diamond. Lavitar can be found on route 207 in the game.
migrate from firered or leafgreen
lucas/dawn little sister at some point will tell you she saw lavitar on news at route 206
Yes you can find it at nightime.
safari zone or kanto
yes you have to do the Pokemon league
level him up to level 30
train to level 25