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In Diamond and Pearl a single [[Lava Cookie]] is given to the player as a reward for finding the Suite Key of a lady at Valor Lakefront. In Platinum she gives the player a [[White Flute]], and states how it is only found in the Hoenn region.
In the one of the trainers in the [[ Seven Stars Restaurant]] comments on how their meal is prepared with a spicy sauce in Hoenn style made from grated [[ Cheri Berry|Cheri Berries]].
In HeartGold and SoulSilver, when the player meets Bill he mentions the Hoenn region, and that he worked with Lanette there.