For those unaware, Palkia and Dialga are the mascots of Pokemon Brilliant Diamond & Shining Pearl, with each one not only appearing on the covers of their respective games, but also playing a pivotal role in the team Galactic storyline that features throughout both. As one might expect by their prominence, they're two of the most powerful Legendary Pokemon of all time and so are definitely worth catching if players are able.
Unlike some of the other Legendaries that can be found in the games, players will need to interact with Palkia (Shining Pearl) or Dialga (Brilliant Diamond) in order to complete the main story, but whether or not they actually catch them will depend entirely on their desire to do so and their ability to make it happen. Indeed, those hoping to capture them without a Master Ball are going to have their work cut out for them due to their incredibly low catch rates.
Where to Find Palkia and Dialga in Brilliant Diamond & Shining Pearl
In order to find Palkia and Dialga, players will need to make their way to the peak of Mt. Coronet. They won't be able to do this straight away though, so will need to wait until after they've beaten Candice at Snowpoint City Gym, visited Lake Acuity, and then defeated Cyrus at the Team Galactic Headquarters in Veilstone City. With all that taken care of, they should stock up on Ultra Balls and then make their way to the upper areas of Mount Coronet by using their recently acquired Rock Climb HM.
After climbing to the very peak of the mountain, players will eventually find themselves in an area known as the Spear Pillar, where Cyrus will summon one of the two Legendary Pokemon. In Brilliant Diamond, it will be Dialga, while Shining Pearl players will instead be faced with the mighty Palkia. Before they can try catching them, however, they'll first need to beat Commander Mars and Commander Jupiter in a double battle with their rival, sit through a short cutscene and then defeat Cyrus in another one-on-one duel.
How to Catch Palkia and Dialga in Brilliant Diamond & Shining Pearl
Once players have beaten Cyrus, there'll be a short conversation with Professor Rowan, after which, they'll be able to initiate a battle with the Legendary Pokemon by approaching it and pressing the A button. Unless they plan on using a Master Ball to catch it, players should definitely save the game before going any further, as if they accidentally kill the Pokemon in battle, they won't get another shot at catching it until after beating the Elite Four. The same is also true if they run out of Pokeballs or accidentally run away after one of their Pokemon has been knocked out.
Given that players received a Master Ball at the Team Galactic Headquarters just a little earlier on in the game, many players typically opt to use it for Palkia or Dialga. This really isn't a bad idea, as with a catch rate of just three, the two Pokemon are among the hardest to catch in the entire series, not just Brilliant Diamond & Shining Pearl. If they've already used their Master Ball or are saving it for something else though, players will instead need to lower the Pokemon's HP and then rely on Ultra Balls.
At Level 47, Palkia and Dialga are fairly durable Pokemon, so players don't really need to worry about killing them with a single attack unless they're massively over-leveled for this point in the game (60+). As the target's HP begins to drop though, players should switch to their weakest moves and start slowly chipping away at their remaining health until it's near the very bottom of the red zone. If they have a Pokemon that can inflict sleep status, this can also be incredibly useful and should boost players' chances quite a bit.
With the Pokemon's HP low and Sleep in effect, it's time to start hurling Ultra Balls until the Pokemon is caught. It might only take one or two, but could just as easily require ten or more, so players should be prepared for a long battle and be ready to heal up their Pokemon when needed to prevent their party from being wiped out. Providing they can keep one of their Pokemon alive and don't run out of Ultra Balls though, players will eventually catch Palkia/Dialga.
Once the Legendary Pokemon has been caught, players should investigate the area behind where it was originally standing rather than leaving straight away. Those playing Brilliant Diamond will find an Adamant Orb there, which, if held by Dialga, will boost the power of both its dragon and steel-type moves. Shining Pearl players, on the other hand, will find the Lustrous Orb, which can be used in much the same way to boost the power of Palkia's Dragon and Water-type attacks.