Life Force (1988 on the NES) took the Gradius engine and added the two things it needed most: a second player and a wild new theme. You fly into the body of a giant organism, blasting through pulsing stages that alternate between horizontal and vertical scrolling.

The lineage is tangled and worth untangling. The arcade original was Salamander in 1986, a Gradius spin-off that threw out the power meter in favor of instant pickups. Konami then reworked it for the American market as Life Force, wrapping the stages in a story about a living planet-sized creature called Zelos. The NES version takes the Life Force theme and puts the Gradius power meter back, so you're once again marching a selector across Speed, Missile, Ripple, Laser, Option and Force Field and deciding when to spend.

Two players changes the calculation completely. Both ships pull from the same capsule pool, so every pickup is a negotiation. The usual arrangement is one player rushing Speed and Options to sweep the front while the other holds back on Force Field to survive the cell walls. There's no friendly fire, but there is a shared screen, and in the vertical stages the screen is not generous.

The vertical sections are the real showpiece. Organic corridors closing in, tentacles sweeping across the gap, a wall of teeth at the end. In 1988, on a console mostly full of blue skies and bricks, flying up somebody's digestive tract was memorable.

And the Konami Code is here too, doing something different: in Life Force it grants 30 lives rather than a full loadout, which is precisely what two players need to reach the end in one sitting.

Fast, weird, and gorgeous for its time. The organic level design still looks striking decades later.