Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:2773405.
This is a remix of the fantastic grip created by zeroordie881. Upon printing that one, I found that the fit was a tad loose from top to bottom and the power button hole didn't quite line up with the actual button. The problem with the loose fit turned out to be because the two small tabs at the top that are supposed to slip into the holes on the rear of the 3ds kept breaking off with the support material. I tried bumps instead, but those too kept breaking off, so I finally just dropped the large tabs down 1mm. Perfect snug fit!
I didn't want to do a remix just for such a minor modification, so I added a slot to allow for accessing the game cartridge slot. I also cut a slot along the edge above the power button so that all of the indicator LEDs can be more easily seen, even with the 3ds closed.