I'll ref! ^^ (This is, if you'd like. I'll still post the arena I choose, so you know what you're getting.)
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Arena: An underwater chamber, deeply submerged. Inside of the chamber, however, there is no water aside from a small pond in the center of the arena. Thick and coiling vines reach up to the top of the dome, then circle around the ceiling. The flooring is dusty dirt, adorned with a few rocks, most large and able to support the weight of a Pokemon. There is a second chamber to the building, though it can only be accessed one way. The glass of the first chamber is sturdy, yet still breakable from intense force of Pokemon attacks. If any of the glass is punctured by an attack, all the glass in the first room of the dome will shatter, then the entire place will flood. Then the battle will take place on the second chamber, until after three rounds, which the glass of the first chamber will magically be restored.

Second Chamber - Sealed away at the side of the first chamber, this area can only be accessed after a flood, then is sealed away once more after both battlers come inside. It's smaller than the first chamber, and the ground is wet and is covered with about an inch of water, until the center of the arena where the land is sloped upwards to form a ground platform and it's covered in fresh green grass, with a tree somehow emerging from the water. And although this place is also surrounded by water, the glass cannot be broken. The ground platform winds around the tree, allowing any Pokemon to reach the top of the arena. After three rounds, the battle goes back to the first chamber.
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^^;; *wonders why I can't be that creative when I'm trying to think of an arena for my own battles. xD*