Pokémon: The Series Rewrite:Indigo League Part 1

Episode 55: Riddle Me This

Ash and the group get on a ship on the way to Cinnabar Island where they arrive and find the gym abandoned and decide to look in the mysterious Pokémon mansion which is revealed to be completely destroyed going through the halls and find a mysterious old man and solve some riddles. They get the key to the gym and head to the gym where the old man is revealed to be Blaine, the Cinnabar Island Gym Leader.