You've beaten Cynthia. You survived that Garchomp. The credits rolled, the music swelled, and you're officially the Sinnoh Champion. But then you realize the real game hasn't even started yet because your Pokedex is looking tragically empty. If you want to unlock the "real" endgame in Pokémon Brilliant Diamond—we're talking Poké Radar, the Fight Area, and those sweet, sweet legendary encounters at Ramanas Park—you need the brilliant diamond national pokedex.
It’s the ultimate gatekeeper.
Most people think you have to catch every single thing you see to get the National Dex. That’s a total myth. You don’t need a living dex. You don't even need to catch 'em all—at least, not yet. You just need to see them. Specifically, you need to see all 150 Pokémon in the Sinnoh regional dex. Once you’ve ticked those boxes, Professor Oak shows up, has a chat with Rowan, and hands over the keys to the kingdom.
The Grind to 150: What Most Players Miss
Honestly, finishing the Sinnoh Dex is less about hunting and more about being a completionist during your trainer battles. If you fought every trainer on every route, you're probably at 140 or so. It’s those last ten that usually cause the headache.
Take Drifloon, for example.
If you didn’t fight the trainers in the Hearthome Gym correctly, or if you just breezed past Valley Windworks on a Tuesday, you're stuck. Drifloon only spawns on Fridays. If it's Monday and you need that entry to unlock the brilliant diamond national pokedex, you're basically looking at a calendar-wait or a cheeky system clock manipulation (though be warned, the game punishes time-traveling by freezing daily events for 24 hours).
Then there’s the "Box Legend" problem. You’re playing Brilliant Diamond, so you’ve seen Dialga. But your Dex has a massive hole where Palkia should be. A lot of players think they need to find a trade partner immediately. You don't. Go talk to Cynthia’s grandmother in Celestic Town after the Spear Pillar events. She’ll show you a book with a picture of Palkia. Boom. Seen. Entry logged.
Why the National Dex Changes Everything
Once Rowan gives you the upgrade, the game basically explodes with content. This isn't just a checklist; it's a structural shift in how the game plays.
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First off, the Grand Underground transforms. Before the brilliant diamond national pokedex, you’re seeing the same Geodudes and Shellos over and over. Afterward? You start seeing non-Sinnoh starters like Torchic, Bulbasaur, and Squirtle popping up in the hideaways. The spawn tables completely refresh.
The Poké Radar Factor
You also get the Poké Radar. This is the holy grail for shiny hunters. It’s a tool that lets you chain encounters by looking for shaking patches of grass. It’s finicky. It’s frustrating. You’ll get to a chain of 39 and then a random Bidoof will break it, and you’ll want to hurl your Switch across the room. But it’s the only way to get certain Pokémon like Tyrogue or Mareep.
Ramanas Park and the Legendaries
Then there’s Ramanas Park, which replaces the old Pal Park from the original DS games. This is where you trade in Mysterious Shards (found by digging in the Underground) for Slates. These Slates let you summon legendaries from Kanto, Johto, and Hoenn.
It is a massive resource sink.
You’ll spend hours—and I mean hours—chipping away at walls in the Underground hoping for a Small or Large Mysterious Shard. It’s a loop: dig, trade, fight a legendary, repeat. But if you want Rayquaza or the Regi trio, this is the only path forward.
The Tricky Entries That Stop Progress
Let’s talk about the ones that actually trip people up. Lumineon is a classic. You’d think a fish would be easy to find, but unless you’re using the Good Rod on specific routes or fighting specific swimmers (like the ones on Route 223), you might miss it entirely.
And don't get me started on Spiritomb.
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In the original games, you needed to talk to 32 actual people in the Underground. In Brilliant Diamond, they changed it to 32 NPCs. It’s still a chore. You have to run around the tunnels, zoning in and out of hideaways to reset the NPC spawns, just to get one encounter at the Hallowed Tower. Is Spiritomb necessary for the National Dex? No, because it's part of the 150. But if you're going for a full 493-entry completion later, it's a hurdle you’ll have to jump.
Manaphy: The Mythical Exception
One thing people often worry about is Manaphy. Since it’s a Mythical Pokémon, does it count? For the brilliant diamond national pokedex unlock, you technically don't need the "seen" data for Manaphy to trigger the event with Oak, but most players got the Manaphy Egg via Mystery Gift early on anyway. If you missed the event window, don't panic. Mythicals like Mew, Jirachi, and Manaphy are usually excluded from the hard requirements for completing the Dex in the eyes of the game's internal "completion" triggers.
Advanced Strategies for Completionists
If you're serious about filling all 493 slots, you need to understand the Swarm mechanic. Every day, after you get the National Dex, you should go talk to Dawn’s (or Lucas's) little sister in Sandgem Town. She’ll tell you about a massive outbreak of a specific Pokémon on a specific route.
This is how you get the rare stuff.
Pidgey, Dunsparce, Slakoth—these don't just wander around Sinnoh. They only appear during these swarms. If you miss the day Dunsparce is swarming, you might not see it again for weeks. It’s totally random.
Also, keep an eye on the Great Marsh in Pastoria City. The "Daily Binoculars" upstairs in the gateway are there for a reason. They tell you which "rare" National Dex Pokémon has rotated into the safari zone for that day. If you're looking for Shroomish or Yanma, that's your only ticket.
Breaking Down the Version Exclusives
You cannot do this alone. Period.
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Brilliant Diamond players are always going to be looking for the Pearl exclusives. You have the Stunky line, the Cranidos line, and the legendary dogs (Raikou, Entei, Suicune). If you want the Lugia or the Birds (Articuno, Zapdos, Moltres), you have to trade with someone who has Shining Pearl.
The community usually uses specific link codes for trading version exclusives. For example, trading a Cranidos for a Shieldon often happens on dedicated "trade rooms" using the Pokémon's Pokedex numbers as the code. It’s a bit of a Wild West situation, but it works better than the random global trade station sometimes.
Practical Steps to Finalize Your Collection
If you are sitting at 148 "seen" and you're losing your mind, here is exactly what you do.
- Check the Swimmers: Most people skip the water routes between Sunyshore and the Pokémon League. Go back there. Fight every single swimmer. They have the Finneons and Lumineons you're likely missing.
- The Celestic Town House: If you're missing the opposite box legendary, go talk to the elder. She is in the large house at the top of the map.
- The Mansion: Backlot’s Trophy Garden is a goldmine. After you get the National Dex, talk to him every day. He’ll "brag" about a Pokémon appearing in his garden. This is how you get Eevee, Porygon, and the babies like Cleffa and Igglybuff.
- The Underground Reset: If you aren't seeing new Pokémon in the Underground, make sure you actually talked to Oak in Rowan’s lab. The National Dex doesn't just "happen"—you have to trigger the dialogue.
The brilliant diamond national pokedex is a massive mountain to climb, but it’s where the game actually finds its legs. Without it, you're playing half a game. With it, you're playing a massive tribute to the first four generations of the franchise.
Get your digging tools ready. You're going to be in those caves for a long time.
To maximize your efficiency, start by clearing the remaining trainers on Route 221 and 222, as they carry many of the "missing" entries like Wingull or Gastrodon forms that players often overlook during the main story sprint. Once those are logged, focus your Underground digging specifically in the larger zones to find the Mysterious Shards needed for Ramanas Park. Check the daily swarm in Sandgem Town every single morning before doing anything else, as those spawns reset at midnight and are easily missed. Finally, use the Link Trade code system to swap your Diamond-exclusive fossils for the Pearl equivalents to ensure your "captured" count keeps pace with your "seen" count.