CHIMERA BEAST / Jaleco / Arcade
Chimera Beast is an odd, unreleased prototype of a game made by Jaleco. It's a fairly standard side-scrolling space shooter, but the twist is that instead of saving the planet from aliens or whatever, you play as a mindless marauding alien trying to eat as many life forms as it can (and basically wreck the planet's ecosystem) in order to grow and evolve.
The game is actually fully complete, though it obviously needed a little more polish in the graphics and gameplay departments. Apparently Jaleco put it before focus groups, and the response was so negative that they decided to scrap the project altogether. I suppose the subject matter might have had something to do with that - after all, you're a hideous creature flying around eating everything it can find in order to mutate into an even bigger and more hideous form. The uninspiring gameplay and irritating music likely had a share to do with it as well, though.
Your little alien marauder starts out with a pea shooter, and the ability to throw his jaw out to eat foes. When you eat an enemy, you sometimes can gain a power from them, such as growing an armored tail to smack down foes who approach from the rear, or the ability to fire homing needles. This "evolution" system is an interesting one that would go on to be copied by games like EVO, but in its early incarnation here it's more confusing than anything else. It's often not clear what type of ability an enemy will give you, so instead of consistently growing a particular ability you just end up with a random weird-looking mishmosh of growths. The powers are easily gained, but also easily lost when you get hit, and in your small unevolved form you are pretty weak. This is also probably the only game ever created that has the grapes to use cancer as a power-up. It's really tough, with a ridiculous slew of enemies being thrown in your face that you just don't have the firepower to keep up with.
The only real reason I can see anyone sticking with this one past the second or third level is to see if you eventually get to start eating humans. I'll spare you the agony - you do, but it's not very exciting. Aside from some little pixely people standing on the ground here and there, most of your humans will have to be consumed inside of a crunchy outer shell of fighter jets.
The game also has a bizarre ending - you fight some other alien mutant thing, but killing it actually gets you the "Bad Ending", as your insatiable life form moves on to destroy yet another planet. No, the way to actually win the final battle is to get killed, and then not continue - and then you get the good ending.
So it's not that great of a game, but it is notable as a rarity, and for its dark subject matter.
* Gameplay Video