The Galaxy Arena is one of the tennis courts in Mario Tennis Open. It is a galaxy-based court that will have objects that appear on it from Super Mario Galaxy like a Launch Star, Star Bits, Shrinking Tiles, a Black Hole, Red and Green Lumas, the Comet Observatory and even a planet from the Gateway Galaxy. The special game Galaxy Rally would also be played on this court. Star Chips would appear in this special game and the player would need to collect them by hitting the tennis ball at them. It can only be unlocked after completing the final cup in the Star Open Tournament.
The unlockable stage would have differences on it from the one in Galaxy Rally. The shrinking tiles would not be there, but instead it takes place in another location. It would have max bounce and max speed. It would have two varieties, the Morph and the Crystal Court. The Morph Court would have an added gimmick. When a player performs a chance shot, and it doesn't get volleyed, then the type of the floor on the opponents court will change to patterns from other courts featured in the game. This will affect the ball velocity and bounce. Only one part of court would be altered and the player would need to perform a chance shot to change the pattern on the opponents court. The Crystal Court would play normally.