Nabbed from: https://www.smspower.org/Cheats/TransBot-SMS

Secret Command

Hold 2 on controller one while powering on the system. Release the button when a screen with the numbers one through four appears. (takes about 10 seconds)

1 (Press Up on D-Pad) = 10 Lives

2 (Press Down on D-Pad) = ARM doesn't deplete (special ammo)

3 (Press Left on D-Pad) = No POWER loss (damage)

4 (Press Right on D-Pad) = Slows down the letters after picking up a ? bubble.

Sometimes it takes a few presses to get it to toggle to "On." Once on though the only way to turn them off is to reset (power off) the system.

Press 1 or 2 on controller two to exit after the desired options are selected.