Ok, this probably deserves a metric ton of explanations. Basically the idea is inspired from a friend of mine who came up with an RPG concept involving atoms, and having antimatter as the final boss. So yeah, I took that idea for this week's challenge, but made several changes.

This is a shooter based on chemistry, and I decided to go for a fairly abstract look for the mockup. The interface is heavily inspired by rRootage's setup, which I rather like. Up to 2 players can play, and either player can choose to be CH4 or ZnI2 as their ship.

CH4: This is slightly inspired by Tumuki Fighters. During the stage, enemies will drop C when they are destroyed, which can then be picked up by the player. Each one adds to the CHN (chain) counter (bottom left), which powers up a "Combust" command (basically a bomb whose power is based on the amount in the chain.) Now the head C is the only C that counts towards the player's life, so the other Cs can get hit without killing the player. However, if a C is hit, then it splits the CH3-(CH2)n-CH3 into two pieces, and the disconnected piece disappears.

ZnI2: This one is inspired by Ikaruga. The ship is either + or - charged, and it can collect bullets of the other type (For convenience, it's just Ikaruga's color matching rules.) However, there's a slight twist in that your ship's charge is tracked (bottom right). If it ever goes above +3 or below -3, then your ship gets destroyed. In addition, your ship's power depends entirely on how unbalanced its charge is (the more unbalanced, the stronger.)

Surprisingly enough the final product turned out to be less messy than I expected (whoo), but just in case I'll cover everything:

Blue diamonds/Big red squares: Enemy bullets.

Shapes with + signs in them: Player ships. Circle represents CH4 and Square ZnI2. The + sign is the actual hitbox of the ships.

Light red square surrounding ZnI2: Charge indicator. Gets larger the closer a player is to +-3, and the color indicates the charge.

Dark blue circles: H atoms of CH4. Each one shoots a bullet.

Light blue circles: CH4's bullets.

Dark red tiny squares: ZnI2's bullets.

Gigantic Black Thing: Antimatter, the EXTRA STAGE BOSS

Hopefully the health bar at the top is noticeable as well.

Bonus material:

http://img.photobucket.com/albums/v396/x0_000/extrastageextra.png