Pokémon Diamond & Pearl feature an extensive Pokédex. While some of these Pokémon originated in other regions, a large number of them entered the series in Generation IV. The Sinnoh region introduced some powerful Pocket Monsters, many of which are still relevant now.
A Pokémon's power can be measured in several ways, including through its base stats and accessible moves. This information can all be found on the website Serebii.net. The stats of some Pokémon have changed since their introductions, and because Brilliant Diamond & Shining Pearl will be a part of Generation VIII, the strength of these Sinnoh Pokémon is based on their current stats.
Magnezone
One of many Sinnoh evolutions to previously introduced Pokémon, Magnezone is a significant upgrade to its pre-evolutions. Its high Special Attack stat allows it to utilize some of the powerful Electric-type moves it can access. It also has a decent Defense and a great Special Defense stat, which means that it can withstand a lot of damage before being beaten by an opponent.
The biggest drawback of using Magnezone is its extreme vulnerability to Ground-type attacks. As long as these are avoided, though, Magnezone is one of the most reliable picks in the region. While it may lack a variety of aggressive attack moves, this Pokémon's Defense skills are impressive enough to be a worthy character to play as.
Infernape
Chimchar could be considered the best starter from its generation, and this is largely due to its final evolution into Infernape. This Pokémon's Physical and Special Attack stats are the same, as are its Physical and Special Defense. This evenly distributed skill set means that players can choose the move category they want to use depending on the matchup, and they do not have to fear damage of either category as both will do the same amount of damage. Infernape is a well-rounded Fire/Fighting-type, and its popularity as a starter is deserved.
Rhyperior
With an incredible Attack stat, Rhyperior strikes fear into the hearts of many opponents. It has an extremely low Special Attack stat, but this does not matter since every attacking move Rhyperior learns from leveling up is Physical.
The biggest hurdles to using Rhyperior are having to deal with its extremely low Special Defense and Speed, as well as its extreme vulnerabilities to Grass and Water. Matchups with Special attackers can be difficult, especially those with types strong against Rhyperior. In battles with many enemies, though, Rhyperior can devastate in one strike, making it one of the best attackers around.
Tangrowth
Generation IV's evolution to Tangela drastically improved the line. Tangrowth's fairly evenly distributed Physical and Special Attack stats allow it to use both categories of Grass attacks with ease. Like Rhyperior, though, its major flaws are its low Special Defense and Speed.
As a pure Grass-type, Tangrowth has several weaknesses, but no extreme vulnerabilities. It also has a high Defense stat, meaning that as long as it is not hit with a super-effective Special attack, it can often withstand several hits. A variety of strong Grass attacks help to make Tangrowth a powerful member of any team.
Mamoswine
A Pokémon with high HP, Mamoswine can stand its ground during battle. This stat helps to make up for its only decent Defense and its mediocre Special Defense. When given the opportunity, Mamoswine shines with moves powered by its high Attack stat. The pocket monster's Ice/Ground typing gives it a boost to these types of strikes. These two types combined are super-effective against nine types, a large portion of the Pokémon in the series. While many attacks are also super-effective against Mamoswine, the Pokémon's bulk and power help it to hold its own against enemies.
Togekiss
Togekiss benefits from having relatively high Defense and Special Defense stats. When Generation IV came out, the Fairy-type did not yet exist, meaning Togekiss was introduced as a Normal/Flying-type. However, once Togekiss lost the Normal-type and gained the Fairy-type, it improved even more. Its high Special Attack stat allows it to utilize some strong Fairy and Flying Special moves. It is now considered to be one of the best dual-type Fairy Pokémon in the franchise, and it is still a consistent member of many players' teams.
Electivire
Electivire has remained as one of the best pure Electric-types since it first entered the series. Its high Speed stat allows it to move before many opponents, and its very high Attack stat lets it take them out in many circumstances. Although the Electric-type is fairly limited, being super-effective against only two types and not effective at all against Ground, Electivire can learn a variety of Physical attacking moves of different types.
While it does not gain a Same Type Attack Bonus from these, its high Attack makes up for this and makes these moves incredibly viable. Even in neutral matchups, Electivire can shine as an extremely powerful fighter that can take on a variety of types in the game.
Lucario
When many people think of the Sinnoh region, the first Pokémon to enter their minds is Lucario. Quickly after its introduction into the Pokémon universe, it became a playable fighter in the Super Smash Bros. series, further cementing its legacy in multiple mediums.
The power often associated with this Pokémon is not unfounded. Although it has a lower base stat total than many other Pokémon in the Sinnoh region, its largest strengths come from its Attack and Special Attack stats. It can also use many powerful moves at an early level. It is clear why so many fans enjoy using Lucario, and why it is often considered one of the best Pokémon in Sinnoh.
Garchomp
Perhaps the best pseudo-legendary Pokémon in the series, Garchomp has been a fan favorite since it was used on the Sinnoh champion Cynthia's team. Its high Speed and very high Attack stats grant it the power to take down many opponents before they can move once.
If it cannot knock out enemies in one hit though, it can still withstand several blows with its above-average Defense and Special Defense, as well as its high HP stat. The bane of Garchomp's existence is the Ice-type, but if it can avoid it, this Pokémon can be unstoppable.
Magmortar
The final evolution of the Magmar line is an incredibly powerful Fire-type even now. Magmortar's high Special Attack stat lets it deal a large amount of damage using the many Special Fire moves it can access.
Being a pure Fire-type limits its potential in certain regards, since it does not gain a Same Type Attack Bonus with moves of any other type, but it can still defeat many opponents using neutral Fire attacks. Magmortar is still highly sought after for many teams, fully capable of sweeping through enemy teams that cannot directly counter it.