Pokémon Crystal - Battle Tower
The Battle Tower is a huge building found west of Olivine City. In the Japanese version, the Mobile Adapter is needed to gain access. In the Battle Tower, you must take with you only three Pokémon (of different species). You’ll also need to choose the level to play by. None of your Pokémon must top this level. The Japanese edition features a chart of the top seven trainers you battled.
In the English edition there are preset trainers with random Pokémon, that can hold items. This makes them more difficult than normal trainers. You won’t gain experience by battling them. You also get fully healed between trainers and at the end of the challenge. If you beat seven trainers in a row, you win five of either Calcium, Carbos, HP Up, Iron, or Protein. You can battle in the Tower any number of times you want each day.
The levels that you can select to battle at are 10, 20, 30, or 40. After you beat the Elite Four and the Champion, then you can choose from 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100. The Pokémon that you use have to be at or below the level you chose. Each Pokémon must be of a different species and hold different items, and Celebi, Ho-Oh, Lugia, Mew, and Mewtwo can enter only Battle Rooms of level 70 or higher. Eggs are ineligible. Using items from the Bag is not allowed in the Battle Tower.