Go to GameFaqs.com and go to diamond, hit walkthough and that will show you how to beat the game from start to finish.
You can't catch Lugia in Pokemon Diamond. You can only get it through trading or cheating.
trade from platnium to diamond through either nwc orthrough having 2 ds systems
Have a strong fire type pokemon.
migrate them through palpark after you get the national pokedex.
i believe there is 490 through 493
You can get it through trade or the GTS.
ar or through an event
You can only get it through events.
You can't find tangela in diamond or pearl you have to transfer it over through Pal park
You can only move pokemon from ruby to diamond, not the other way around, through pal park. You need both games in your ds to do this
Pokemon diamond
ARCEUS get it through event