Very creative game and it's fun.
I play ZX Spectrum games on MiSTer, but I wonder why you still have to use the keyboard to jump when you use a joystick (Kempston). That's why I assigned the X key (jump) to joystick UP, the Z key (attack) to the fire button, and K (down), J (left) and L (right) on MiSTer's Speccy core and chose keyboard in the game.
Here is my gameplay from it: