Mario Tennis Open is the first 3DS installment of the Mario Tennis series, and the first handheld entry to be in full 3D and the first period to support online multiplayer.
Most of the playable cast from Mario Power Tennis returns, but a number of others were removed and replaced by new playable characters. It is also possible to play as a Mii, and use StreetPass to challenge other Mii characters in seven point matches and Ring Shot mini-games.
Also a first is a load of unlockable costumes and accessories for your Mii only, some costumes of which are unlocked after beating StreetPass Mii characters a certain number of times in a row. Accessories are bought in the shop after unlocking them after beating opponents in the various cups.