Yes you can find it at nightime.
safari zone or kanto
Mt. Silver. Lavitar is around level 20!
You can't
you can't
Mt. Silver
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.
entine does not exist
migrate from firered or leafgreen
You can't evolve Togetic in Pokemon Crystal as Shiny stones did not exist in Crystal. Togekiss was also introduced in Gen4. Crystal is Gen 2?
lucas/dawn little sister at some point will tell you she saw lavitar on news at route 206
There is no such thing as a Crystal Onix. It only exist in the anime.