Do you want a Reshiram? For PvE? Yes, it’s a great counter, worth getting, a top fire counter with it’s exclusive move Fusion Flare in fact!
Ground, rock and dragon are your hard hitting moves here, fire and dragon typing cover a lot of its weaknesses, big hitting dragons always come out, even when return damage is super effective!
Go to the official counters page for a complete list including Shadows and Megas to see how your Pokemon perform.