Eterna City, one of Sinnoh's oldest cities, along with Celestic City is very prosperous and hold true to Sinnoh's great legend of the Regions creation. The City is west of the Eterna Forest so it provides the city with clean, fresh air. Speaking of fresh the City's Gym Leader is a master of Grass type pokemon even though you might find bugs to be pesky they can be helpful in this battle so you should probably utilize the bugs from Eterna Forest for this battle.