Appearance: A bigger variant of a standard enemy.
Abilities: More HP, Strength and less likely to get Stunned.
Weaknesses: Very slow and weak to all elemental attacks.
Note: Probably the first and most common Elite foe you will come across. Learn how to deal with them from the start and you will spare yourself a lot of trouble in the future.
Generally what you want to do is kill the smaller, faster enemies first since it is rather easy to avoid him due to his reduced speed. Just keep your distance and you will be fine. Once you did that, it is time to take him out. I recommend aiming for the head and stunning him, then following up with a melee attack and finally finishing him off with another melee attack while he is down on the ground.

Appearance: A smaller variant of a standard enemy.
Abilities: Increased speed, also less likely to get Stunned.
Weaknesses: N/A
Note: Watch out for them speeding towards you and I mean it. Just aim for these enemies first.

Appearance: Covered in flames, literally.
Abilities: Burns anything it touches and explodes upon death, burning anything that happens to be close at the time.
Weaknesses: Ice based attacks.
Note: Generally as with most enemies keep your distance and try to have them close to other enemies before delivering the finishing blow so they die in the explosition or at the least take som damage, saving you some precious bullets. Also if you finish them off with a melee attack you will take no damage so don't be afraid to melee them if you see that they are stunned.
Extra note: Burning characters take damage over time.

Appearance: Covered in ice (blue).
Abilities: Freezes aything it touches and explodes upon death with the same effect.
Weaknesses: Fire based attacks.
Note: Same as "BURNER".
Extra note: Frozen enemies are slowed. Frozen player characters are left immobile for a very short time during which they also take damage over time.

Appearance: Emits electricity.
Abilities: Shocks anything it touches and explodes upon death with the same effect. Has a tendency to run and is faster.
Weaknesses: N/A
Note: Same as "BURNER". Prioratize this enemy as it can speed in towards you almost like a "SPRINTER".
Extra note: Shocked characters take extra damage from every attack.

Appearance: A huge force field is present in the front of the enemy. Impossible to miss.
Abilities: Protects himself and any othe enemies that are directly behind him with the shield.
Weaknesses: Attacks from the sides and back deal normal damage.
Note: The shield renders frontal attacks almost useless as the damage done is greatly reduced but don't shy a shot if it has low health since it does not completely negate the damage and you can still kill it. Of course, having two players makes dispatching these foes an easy task but if you are solo, I suggest aiming for the legs or using a shotgun to knock this enemy down and then make sure you go to the legs to melee it for heavy damage as meleeing from the front usually hits the shield and does far less damage.

Appearance: They have a red field around them which signifies the area of effect.
Abilities: Once you get too close to this enemy, a countdown (usually 30 secs) will appear along with it. When this timer reaches 0 you will be dealt fatal damage, in others words, die.
Weaknesses: N/A
Note: Always keep a lookout for these enemies since failing to do so will result in a Game Over unless you want to waste your precious Life Crystals. When this enemy appears forget whatever you were doing and just focus on taking him out, preferably from a distance as doing so will keep you save in case something goes wrong. If the timer appears then there is no more reason to keep your distance, get in close and personal.

Appearance: N/A but a green gas emits from the enemies that the "HEALER" is / will be healing.
Abilities: Constantly heals other nearby enemies.
Weaknesses: N/A
Note: Always prioritize this enemy since if you don't take him out, you will likely waste a lot of ammo, if you will be able to kill anything at all, that is.

Appearance: N/A for the enemy itself but purple/pink lines are attached to the enemies that the "BOOSTER" gave new abilities to.
Abilities: Grants a random ability to nearby enemies.
Weaknesses: N/A
Note: These are the guys you want to take out after you dispatch the Healer since they will make a fight a lot longer than it should have been, giving regular enemies abilities that should not be there in the first place. But don't worry even if it grants abilities to an enemy, as soon as you kill the "BOOSTER" any abilities it gave will disappear along with him and the other enemies will return to their original form.

Appearance: Green gas cloud emitting from their feet periodically.
Abilities: If you get in contact with the gas cloud you will take light damage without them actually attacking you. The longer you stay in the gas cloud, the more damage you will take.
Weaknesses: N/A
Note: Just keep your distance, aim for the legs and knock them down.

(3rd icon in the image above)
Appearance: A slowly flashing light surrounding it.
Abilities: Pulls the player character closer to itself.
Weaknesses: N/A
Note: Try taking them out from a distance or get an object in between yourself and the enemy so the ability becomes useless.

Appearance: Silver.
Abilities: Greatly increased Defense.
Weaknesses: Low HP and Weak to Critical Hits.
Note: Grants a huge XP amount upon defeat. Just know them down and then do a follow up melee while they are on the ground, they don't have any resistance to that.

Appearance: As the name sugges, they look as if they were made of gold.
Abilities: Same as "COAT OF ARMOR".
Weaknesses: Same as "COAT OF ARMOR".
Note: Same as "COAT OF ARMOR" except grants huge Gold amounts instead of XP upon defeat.

(3rd icon in the image above)
Appearance: A white light in the center of the enemy that grows brighter as it is charges the attack.
Abilities: Emits a shockwave that disarms the player character.
Weaknesses: N/A
Note: Before the attack there is a short period of time so you can change your weapon to something you don't mind losing but either way don't worry if you lose your main weapon as you can still pick it up afterwards. Just keep your distance and you don't have to worry.

Appearance: Invisible.
Abilities: Invisible.
Weaknesses: N/A
Note: This enemy is completely invisible, if you wish to spot him you have to aim your gun at him.