in platinum after you have gotten national dex go to victory road in the room the guy was blocking and find and catch dewgong
You catch DEWGONG on the battle park island. Just go there use surf and eventually you will find 1.
To be able to catch your Dewgong, you'll have to surf in the water areas to the right of the Pal Park, so make sure to bring a Pokemon who can surf!
The best way to catch a Dewgong is to walk in the Icefall Cave entrance. There, you have a 20% chance instead of the 5% or 10% chance that you get in other places like the Seafoam Islands.
There are a few places you can find a dewgong in on Pokemon Platinum version. You can find him on Victory road, route 226, and route 230. If you catch a Seel you can also get Dewgong by leveling Seel up to level 34.
Dewgong can be caught at the Seafoam Islands and Icefall Cave. Your best bet is to catch one at Icefall Cave, as it has a 20% chance of appearing there.
Catch a Seel on route 226 & 230 (while surfing). It evolves at level 34 into Dewgong. Catch Articuno. Catch Regice.
At SEAFOAM ISLANDS. There you can find Pokémon like SEEL and DEWGONG.
Dewgong cannot not evolve.
I'm not sure but if you know can you please improve it
The pre-evolution of Dewgong is Seel. Seel evolves into Dewgong at level 34.
Dewgong evolves from seel
you can only find Seel i believe... then you can evolve it to a dewgong, I highly doubt you can find a wild dewgong =/