I'm assuming that by "arcus" you mean "arceus". You can't get Arceus except from special events held by Nintendo, or by cheating and using Action Replay.
darkrai and arcus
If you are looking for Arcues you need to trade it with either Diamond or Pearl Version.
(by a can of beans)The best Pokemon in Pokemon
you have to trade it over from platinum because it is not in the unova pokedex
Indeed you can. Arceus however is only available in Pokemon Diamond, Pearl and Platinum's special distributions events. You can check pokemon.com for the latest information on this pokemon :]
You can find Pidey in a Pokemon Outbreak in Pokemon Diamond
you cant
you need a event or action replay. hope i helped(:
Special event on spear pillar
where do i find a totodile in Pokemon diamond/pearl on nintendods
You can not find or get manaphy on Pokemon diamond but you can by hacking, trading or... if you have Pokemon ranger you have to complete the manaphy mission and then you can put it onto diamond.
You can't find a Ho-ho in Pokemon Diamond. You have to migrate.