Reshiram is a Legendary Pokémon, which means that in Pokémon Go you will only be able to catch it during five-star raids. You can participate in these five-star raids in limited time and when they become available, they are the most difficult encounters available in the game. Not only do you need a raid pass to access it, but you will likely need at least four or five friends to help you defeat it.
Weaknesses of Reshiram
Reshiram is a Dragon and Fire type Pokémon. It will be weak to the other Dragon types, along with the Ground and Rock types. It is strong against Grass, Ice, Bug, Steel, and other dragon types, so among your available options, you may want to avoid taking other dragon types in the encounter. You have better ground and rock type options and there are several options available.
Pokémon attach themselves to Reshiram
For those looking to tweak the weaknesses of Reshiram Ground and Rock, there are plenty of options that fit the bill. The best include Rhyperior, Tyranitar, and Garchomp.
Rhyperior is a Ground and Rock-type Pokémon, which means it probably won't take too much damage against most of Reshiram's attacks. Of the available attacks that a Rhyperior may know about, the best choices include mud slap and earthquake, stone crush and edge, or stone demolition and demolition, the latter of which is an exclusive Community Day move. While rock wrecker is the best option, not everyone will have access to it. Earthquake and stone edging are still excellent attack options.
Tyranitar is a Rock and Dark type Pokémon. While it doesn't have that many Rock-type moves to potentially use against Reshiram, it's still a superior choice. You can use one that knows how to crush and cut the stone edge, bite and stone edge, or crush and crush. The bite and crunch won't be as effective as Reshiram because they are Dark-type moves, but if you have a powerful Tyranitar, they are a good choice to have in your lineup.
The excellent final choice is Garchomp, which is a Ground and Dragon type Pokémon. Among the options, it is a double-edged sword because it is weak to any of Reshiram's Dragon-type attacks, but Reshiram is also vulnerable to them. It's a good option for those who want to take a risk, especially against a Reshiram using non-Dragon-type attacks constantly. The best moves a Garchomp can know include Dragon Tail and Earthquake, Mud Throw and Outrage, or Dragon Tail and Outrage. They are all excellent choices because they move state-type-attack-enhancement (STAB) type.
If you don't have any of these options, you can always choose one: Groudon, Rayquaza, Hazorus, Rampardos, Salamence, Paiki, Terrakion, Dialga, Excadrill, Dragonite or Golem. Each of them is a solid option for you when you commit to this raid.
After completing the five-star raid, you will receive a series of premier balls based on how much you contributed to the raid, if you did so with coaches who are friends of yours, or if the raid started at a gym owned by your team. Any five-star raid is available to all players with a raid pass, but they spawn only for a limited time and rotate our Legendary Pokémon residing there. Developer Amazon Games may release additional hotfixes and patches in the future to help optimize the software and ensure a better experience for players.