Walkthrough
The final Pokemon Gym you will need to help save is the one located in Hammerlocke. When you arrive at the Gym, you will see Sonia outside the Energy Plant. Apparently, Sordward and Shielbert are within it with the Wishing Stars, but she can't get in. First, you must help Raihan with a Dynamaxed Pokemon found within the Stadium to his Pokemon Gym. Again, you will have to defeat this Dynamaxed Pokemon all of your own. This time, the Dynamaxed Pokemon will be a Level 62 Haxorus, one that will know the moves Outrage, Earthquake, Iron Tail, and Giga Impact (also being able to use the Max Moves associated with each of those attacks).
After helping clear his Pokemon Gym, you will receive Raihan's Rare League Card.