We're playing it through local wireless connection, and after we booted in the game, we went to the Competition mode, they were 2 options available , the Solo mode and the Multiplayer Mode, so we clicked on the Multiplayer mode and they wrote there Waiting for Other players on both of our DS system, but we couldn't seem to connect to each other..
The games aren't patched, we're both using DSTTi and the latest Firmware waire YSMenu latest infolib fix
Is the D-Play option for the Cooking Mama 3 rom on? You need to turn it on to play local wireless... I had the same problem but with other games (about 3 of them) and I discovered that the D-play for those roms in my Flashcart was actually off... After turning it on, I was able to play wireless