The following is a list of all enemies found within the game, in chronological order.
Positive Cell (Red Enemy): First enemy in the game. A very basic enemy. Drifts along in the same direction perpetually. Is larger than the Negative Cell but moves more slowly.
Negative Cell (Green Enemy): Behaves the same way as a Positive Cell, but is smaller and faster.
Repliclone Cell (Purple Enemy): Be careful! When you shoot this enemy, it splits into 4 smaller cells. Appears in Level 2.
Death-Rupture Cell (Gray Enemy): First enemy to actively target the player. When shot, it explodes and leaves behind a puddle of toxic black ooze. Appears in Level 3.
Positive Plus (Dark Red Enemy): Behaves the same way as a Positive Cell but takes 3 hits to destroy.
Negative Plus (Glowing Green Enemy): Behaves the same way as a Negative Cell but takes 3 hits to destroy.
Giga Cell (Orange Enemy): A slow-moving but gargantuan enemy that takes 5 hits to destroy.
Charge Cell (Light Yellow Enemy): Watch out! Moving faster than the speed of light is the Charge Cell. It chases after the player at a very fast velocity.
Swing Cell (Yellow Enemy): Behaves like a Positive or Negative Cell at first, lazily floating along, but has two smaller cells that swing around it. After one hit, said cells disappear and the Swing Cell gets aggressive and chases the player.
Ghost Cell (White Enemy): All this guy does is chase you, and nothing more. Simple, right? Except that it has the ability to turn invisible. And Ghost Cells cannot be killed while invisible! >:D
The Other Cell (Blue Cell): Unlike all the other enemies, there are no achievements regarding this one, and spotting one is very, very rare. It's also the same color as the player, so it could be a glitch... This enemy behaves just like a Positive or Negative Cell.
There are 7 badge tracks. They are fullfilled by obtaining the achievements that fall into each category. The more in each track you get, the higher level the badge is. Special bonuses are unlocked for reaching a certain number of achievements.
At 20 achievements, you unlock a power-up that kills all enemies on the field.
At 40 achievements, you unlock a power-up that gives you a shield.
At 60 achievements, you unlock an ability that gradually regenerates your health.
Gold bullets that do extra damage are unlocked when you unlock all 77 achievements.