The allies.

Allies appears at some levels, but often you have to build them first. Warning: this page can has spoilers.

Plasma cannon turret:
This is your first ally. It is appears at level 1 and other levels. Plasma cannon turret has Plasma Cannon.

Heavy Plasma cannon ally:
This ally is next after Plasma cannon turret. It is appears at level 2 and some other levels. This ally has Heavy Plasma Cannon.

Rocket launcher turret:
This ally appears on level 3 (after Heavy Plasma cannon ally) and some other levels. This ally has Rocket launcher.

Secret weapon ally:
This ally appears on level 7 (after Rocket launcher turret). This ally has Secret Weapon and it is pretty strong.

Light Plasma Machine-Gun ally:
This ally appears on level 10 and no somewhere more. Its has low health, but can move speed and has Light Plasma Machine-Gun.

Plasma Machine-Gun ally:
This ally appears on level 10 and no somewhere more. It is has got Plasma Machine-Gun.

Plasma cannon ally:
This ally appears on level 10 and no somewhere more. It is has got Plasma Cannon.