Conflict is an unavoidable reality of survival on Na Pali. The following creatures, both native and foreign to the planet, are often more cunning and collected than mere wildlife, yet just as single-minded in their pursuit of your demise.
Long ago the Krall were enslaved by the Skaarj like the Nali. Now, the Krall are willing servants of the Skaarj, and are all too happy to carry out the Skaarj's dirty work. Krall are often seen as guards in captured Nali strongholds, and are seen to patrol these places swinging their concussion staffs as they go. As fighters, they possess two attacks; a whack with the staff close up, and an energy bolt further away. To a limited extent Krall can dodge your shots, but they are not as agile as Skaarj. They make up for this by attacking in numbers. Krall are determined fighters which will continue to attack even if you chop off their legs.
Krall Elite are stronger and more highly-trained versions of your basic Krall guard. These elite fighters are often placed as commanding officers of groups of regular Krall, and are seen to charge with the troops. These blue-tattooed versions carry a more powerful concussion staff that shoots projectiles at a greater velocity. Krall Elite dodge more and take more punishment, so be prepared for a fight.
Mercenaries are rivals to Skaarj supremacy. Skilled at fighting in teams and building huge facilities, Mercenaries are formidable opponents armed with a machinegun, rocket launcher and invulnerability shield. At close range, they will fist you. Fortunately, most Mercenaries can't fire whilst under their invulnerability shield, so you do have a fighting chance. Mercenaries are quite nimble and can dodge your fire but not very effectively. Basically, lay into them until they're dead, but don't waste ammo whilst they're protected by the shielding.
These guys are tough. They are like regular Mercenaries, but these blue-clad Mercenaries are more intelligent, stronger and have more health, but worst of all they can fire whilst using the invulnerability shield. This gives them a major advantage - if there's one creature against which you have to fight strategically, then it's this one. Fight carefully, or you'll be dead faster than a stepped on Nali Rabbit.
Lesser Brutes are the weakest breed of the Skaarj-engineered group known generically as "Brutes". These pink-skinned creatures are the first real opposition that you'll meet. At long range they fire rockets, close up they whack you with the flats of their guns to quite considerable effect. Where you have the advantage here is the Lesser Brute's lack of speed and its relative fragility. Plus, Lesser Brutes don't generally have the intelligence to lead you with their rockets. Make the most of it!
Basically, a larger and more powerful version of the Lesser Brute. Brutes are later-game enemies, being rare in the early maps, only appearing once in the Rrajigar Mine facility. They are all over the place at Dasa Pass and the Nali Castle but that is later on in the game. Anyway, their rockets and swipes are still powerful, and they have more health; they still don't lead you with rockets but it's easy enough to get hit. Identification: beige colour, as opposed to a Behemoth's light blue. More armour than a LesserBrute.
Relatively rare, until Return to Na Pali's Foundry Tarydium Plant. Behemoths are more powerful versions of Brutes that take a lot more damage and can lead you with rockets. They are huge, which is a disadvantage to you, but it does have the one benefit that they are less manouvreable. Behemoths are tough, but you won't meet them too much. Identification: huge size and pale blue armour.
Even your own planet has turned against you. Only in Return to Na Pali, these elite Terran fighters beam down to terminate you as a security risk after you locate the bridge communicator of the crashed UMS Prometheus. Armed with either a Combat Assault Rifle or Rocket Launcher, they attack in team waves to provide opposition that is not only fast and deadly, but is intelligent and can pick up items like Health Packs and dead comerades' weapons to boost their fight. Plan the fight carefully or you're in trouble.
The 30' tall Titan is a humongous enemy that you'll only meet once in a while. It is truly a creature to be feared, as not only do its huge fists pack an immense punch, at long range it fires instant kill boulders at you. Get in the way of one of those, and you really are in trouble. To make matters worse, they stomp along causing the earth to shake, and wallop the ground to send you flying out of control, only to meet a well-placed boulder. Ouch. My prescription, even though Titans have extra resistance to explosives: Eightballs, and lots of 'em. Work down through your weapons after that, but don't use the Minigun (waste of ammo), and save the Flak Cannon for Skaarj and Brutes etc.
Of course, where there's something big there's always something bigger. The colossal Stone Titan is a variant on your basic Titan with stone armour plating such that it takes dramatically less damage from your weapons. I still recommend Eightballs, but don't expect Eightballs alone to do the job. Keep going - like with Titans you can tell you're nearly there when it starts showing pain - until finally the battered giant moans and collapses. Then you've done it. But of course, Return to Na Pali's "Watcher of the Skies" on hard skill has two of 'em...