List DS buttons and specify GBA button (so you could, say, specify both DS L and DS Y to map to GBA L)
Allow mapping of 1 DS button to 2 GBA buttons (i.e. DS Y presses GBA B + GBA L. Games like Street Fighter Alpha have punches as Light Punch: B, Medium Punch: B+L, and Hard Punch: L. It would be nice to map each to their own button)
Title should be pretty self-explanatory, opening this issue for the sake of tracking such a feature (which existed in GBARunner2).