Well, seeing as how Acekard 2i has died a while back and the card compatibility list hasn't been updated in over two years...what should I get for a 3DS compatible card? I still have quite a few games I want to get through, such as the third Mario & Luigi game as well as Black/White 2 and the fan translation of Ace Attorney Investigations 2..
Just buy a cart that still receives routine updates from the producer, or buy one that can use WOOD R4 or YSMENU as it's secondary firmware. And you should be good to go to play those NDS game rom. As for playing 3DS game rom, you'll need either Gateway 3DS or R4i 3DS Deluxe which needless to say requires a 3DS console running a firmware below v.4.5.
There is no hope for Acekard card , they have stoped updating, so better get one another cards , for DS games, r4i gold 3ds is the best one. For 3DS roms, r4i gold 3ds deluxe editon has a good price performance. I'm lucky and found OZ3DS online store.
you can't. There are flashcarts available for 3ds that can play some 3ds roms, but the system can't be emulated by another system yet.