Jet Force Gemini would be a piece of cake if it weren't for those pesky enemies. Here's a list of their names and how to defeat them.
Drones[edit]
They're you average, run-of-the-mill enemies that are extremely common and very easily defeated. While there are varieties and differences, the blue ones are the basic type. You can take them down with anything: machine gun, pistol, grenades-you name it. Blue Drones, unfortunately, do tend to roam in packs, so be prepared to massacre these bugs with a few hits of your preferred weapon.
Sniper Drones[edit]
These suckers are green and actually hide in high places like the treetops (Goldwood) and ledges (mostly everywhere else). Unlike their blue counterparts, Sniper Drones will, for the most part, not attack you in groups. There are few exceptions, but again, they are few. Take them down with one hit of your pistol (preferred).
Ninja Drones[edit]
Ah, the ever-annoying Ninja Drones. These guys are brown in color and a pain to encounter. If you enter an area with a Ninja Drone in it, whatever you do, DON'T HESITATE. These guys will start shooting any Tribals in the area, so dispatch of them quickly. Fortunately, they don't appear very often in the entire game. Send them back to where they belong with the help of your trusty machine gun.
Coward Drones[edit]
These guys are yellow, and as their name implies, utter cowards. The only difference between these Drones and the others is that these guys put their arms up in surrender and throw away their gun as soon as they see you. However, if you turn your back on them, they will throw grenades at you. Kill them (if you wish) to get a red Gemini AKA full health.
Rhino Drones[edit]
These Drones are a more resiliant variety than their blue cousins. Their appearance is slightly different and so is their stamina. Fortunately, they can be gunned down with the Machine Gun or Tri-Rockets. Alas, they tend to roam in groups (come to think of it, don't most Drones roam in groups?), so take them down quickly unless you want your health to rapidly decrease.
Stag Drones[edit]
These are the first big Drones you actually encounter (SS Anubis). They're huge, purple, and will drain your health like crazy if you don't get rid of them quickly. Fortunately, they tend to come in groups of one, so hurry and take them down with your Machine Gun.
Cyclops Drones[edit]
The very first aerial drones you will encounter. These suckers are to the aerial drones what regular Drones are to the Drone family: basic. They can be shot down very easily, but they (like blue Drones) tend to come in bunches. Use your Machine Gun or Homing Missiles to take them down.
Arachno Drones[edit]
These are the second type of aerial drones you will encounter, and, as their name implies, look like spiders. Most of them can be pretty stupid (their AI isn't very advanced) and can sometimes hover in the air while doing nothing. These guys (and all aerial drones in general) come in big groups, so take them down as fast as you can.
Rotor Drones[edit]
These guys are not like your average aerial drone; they actually only rise for a few seconds, then slowly float to the ground.