Mt. coronet, or if you'd rather do it without going through so many weak Pokemon that you might not be able to use then you can level up Snover and you can catch them in the route on the way to Snowpoint City.
You catch it at the top of snow point city.
catch one near snow-point city or evolve sneasel
you can't catch regice in Pokemon diamond, however, with the use of all the regi's traded over you can take them to the temple in snow point city and awaken regigigas
ice/snow types
in the temple in snow point
You have to go to snow point city to catch him
12th January snow point city
snow point temple. two rare Pokemon
no
As far as I know you can't.
when you defeat the Pokemon league and get your national pokedex.
you take them to pal park on Pokemon peal/diamond then you take them to the tempele in the snow go to the bottom floor and click on the big thing and it will battle you but it will be at level 70 it is a normal Pokemon and good luck