Of course, throwing Pokéball at it. But if you mean where, you can't get it in Pokémon Diamond.
you can't catch it in diamond, only in pearl
Bagon is only available in Pokemon pearl. You can however catch a Larvatar instead of a bagon. you can trade one for a Bagon because another pearl player will want one.
In route 210, use pokerader.
You can only catch bagon in pearl. But you can catch larvitar, route 207, you have to use the poke rader. If you had pearl you would find bagon on route 210 (fog) with the poke rader.
you can't catch it in the wild, but you can get it through a trade or pal park.
You can only get bagon in pearl. (and other GBA games) But you can catch lavitar on route 207. If you use the poke rader. They are kind of rare.
No where but in PEARL you can catch a BAGON route 210 with a pokeradar.
shelgon is uncatchable in diamond. U have to catch a bagon in pearl and evolve it and trade.
You can't catch it in Diamond, only in Pearl. But hey, you can catch Larvitar in Diamond but not in Pearl. It evolves into Tyranitar which is stronger. It's in Route 207 and you need to use Poke Radar.
It is possible to catch a Bagon on Pokemon Diamond if you have the Pokeradar. You can find them in Route 210.
first you go to route 210 use defog then you use poke radar in any part of the grass and to catch bagon you use a quick ball or a timer ball and if its night time use a dusk ball.
I know you cant catch a Bagon in Diamond cuz i wanted one to evolve it into Salamence and foud out that they arent even in Diamond