I've added a 6-button gamepad for the new pico-8 just incase that it could be for the key configuration mode can be different than before, the o and x buttons work for the original games, but if you make your own game for the slash and heart including shoulder buttons then this would have been special, so here are the numbers for the buttons.
Slash = 12 (turn into 7) key(C)
Heart = 13 (turn into 8) key(S)
Left Shoulder = 14 (turn into 9) key(A)
Right Shoulder = 15 (turn into 10) key(D)
I've hope you'd like this.