Once you get to the rustling bushes, they allow you to walk on the ceiling - go a little further towards the walking plants and you should find a maze-like area full of rustling bush mimics. Once you’re through that you’ll exit next to a save altar and a boss arena on the left - go right instead and use the bee-ladies to get up on the ledge and continue upwards until you reach a magical gravity lift. The mouth shopkeeper should be up there on the right
Hope it helps :)