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Mr. White (Japanese: ホワイト White) is a character in Celebi: Voice of the Forest.
The group first meets White when Ash is about to miss the riverboat (literally) and White is the one to catch Ash before he hit the water, pulling him aboard to safety with Brock's help. When he finds out their interest in Pokémon, he suggests taking them to his hometown, Arborville, a treetop town much like one location in Hoenn. His watercraft is also a flying boat, the foils becoming inflated and capable of lifting the boat (and at least seven average-weight passengers) into the air.
He is seen again later when Diana and Towa ask him to take them to the area of the forest wracked with explosions. By the time they find Ash, his friends, and Sammy, the Iron-Masked Marauder is already beginning his rampage on the forest, with Celebi under his control. In consequence of following them, the boat is destroyed in the confrontation with Celebi's wooden monster.
White is a witness to the remaining events of the movie, not above the use of violence as he's shown to be threatening the unmasked Iron-Masked Marauder by cracking his knuckles, and during the credits, flies the kids back to town in a new boat. Whether it's a new boat or not is speculation, since both have the number 17 on the hull, but the damage sustained to the original one makes it unlikely to be the same.