Hi guys. I've been following this thread for a few days. It's really frustrating to see that so many of us are having this problem.
I also have a 3DS XL. It's red, standard edition. I have Pokemon Y in cartridge form, and Mario Kart 7 and SSB downloaded through the eShop.
I also called Nintendo on the release date to report this issue. They told me to repair the game, then delete it and redownload, then advised me to wait a few days to a week and see if Nintendo addresses the issue. If all else fails, I would have to send in my system. While my system is still covered under warranty, I think it's total BS that any of us should have to send in our systems, free of charge or not. This is obviously an issue that Nintendo created. I don't know if it requires a patch, I don't know if it requires that the system be taken apart. Whatever the issue, lets hope Nintendo will step up and take care of it in an appropriate manner.
My crashing issue seems to be less mild than what I'm reading here, and I only say that because I sometimes experience periods where I can play for hours on end without any interruption. When the game does crash, it always happen at one particular spot. It crashes in any mode, except streetpass. For example, when I choose Classic mode, I will reach the character screen, select one, move to the stage select screen, select one, and the next screen will contain some sort of game tip. It is on that game tip screen where my game crashes. It doesn't matter what mode, character I choose, stage, random selection, or whether WiFi is on or off. It happens in character and Mii customization modes, as well.
Like I said earlier, I do have periods where I can play for as long as I want. Those periods of time seem to come about an hour-two hours after the game has crashed repeatedly. I will set the system down, come back to, and for some reason the game will actually play and I will not have one single crashing issue. I may experience an internet connectivity issue, but I don't think that's related. I have noticed one thing, though. The last two times I had periods where I could play, my battery was fully charged. For example, this morning I picked up my DS and attempted to play. No luck. It was still connected though. I unplugged the charger, turned it back on, opened up SSB and it played. I was only able to play for 10 minutes since I had to get to class but there were no issues. I came back to my DS around 4 or 5 hours later. I turned it on and it wouldn't play. I plugged in the system, just to see if I would have a repeat of this morning. It charged quickly, turned it on with the charger still connected, and it wouldn't play. I disconnected the cord, tried again, and sure enough the game loaded and played fine for several hours. Also, my screen brightness was at 1, power saving is off.
Sorry for typing a novel here, but I figured it would help if I was super specific. As I'm typing this, I'm attempting to reproduce the same results that I was having earlier today and I'm not really having any luck. The game is crashing with the charger plugged in, and with the charger removed. I'll attempt it again in 10 minutes and see if anything changes. - 1:50am
10 minutes later - 1:59am
Still no luck. Really not sure how I'm having these in and out periods. I'm guessing that tomorrow morning I will turn the console on and I will be able to play. I say that because that seems to be the trend. I'm wondering if theres some sort of power issue, which could explain why a full charge has been the possible solution to the game crashing, along with the low brightness setting.
Anyway, I will let you all know tomorrow. If anyone can think of any ways to further test, I'm all ears.