Minimum amount of badges to get the National Dex in Diamond?

Question

I'm replaying Diamond for the story and put a lot of thought into my team. I decided I want to be the OT of an Elekid which must be in an Ultra Ball (I know I'm being stubborn but the heart wants what it wants...)

Anyway. I've been doing research and found out this will only be possible if I get the National dex to unlock dual-slot mode. I'm okay with this as long as it's not too late in the game. I hope this isn't just a pipe dream.

...so what's the minimum amount of badges I'll need for the National Dex?

Answer 1

You first have to see all 150 Pokemons in your Sinnoh dex. Then you need to go to professor rowans lab and then he will give you a national dex. You can get the national dex before the Elite 4.

Source

So I believe it's technically possible to get the National Dex with no Badges, though it would involve heavy amounts of trading. It gets easier the more Badges you get, but it seems to be obtainable at any time after arriving the Regional Pokedex.

If you cannot trade, then you must have all eight Badges to see Pokemon like Machamp (credit to sumwun).

Hope I helped!

Comments

If you can't trade, then I'm pretty sure you need all 8 badges to see certain Pokemon like Machamp.

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And I believe you need to beat the champion for Azelf, Mesprit, and Uxie

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My answer assumed you were able to trade, I'll edit that.

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You need only 7 badges to get Azelf, Mesprit, and Uxie.

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Oh, really? Intresting

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I used Pokegen to fill my Pokedex and Prof Rowan did not give me the national dex :(  I guess I need to beat the Elite Four.   
I'm just gonna use a random .sav from the internet, catch one and change it's ID and Secret ID then trade it to my cartridge <_<