I'm not sure if it still works, but when Dr. Mario Online Rx first came out I was able to download a trial version of the game and play online with a friend. In fact, I'm sure I still have it on my SD card.
Already have Kirby's Dreamland and Dr. Mario Online Rx, so no real desire to get Dr. Mario Express. I don't own Majora's Mask in any form, though I really don't desire to. However, I have a lot of coins to spend and nothing to spend them on at the moment, so...I might get that.