The Stalker is a type of creature introduced in Borderlands 2. It has the unique ability to vanish from sight. This ability is possible due to a special organ all stalkers have known as the Sach's Organ. This organ stores an electrical charge and is located within its vestigial wings. While hunting or hiding, a stalker's Sach's Organ generates an electrical field which allows it to blend into the environment. When a stalker runs out of electrical energy, the electrical field dissipates. To regenerate an electrical charge a stalker converts sunlight using the solar plates lining its back.
Stalkers vanish when they detect prey nearby, then proceed to creep up on their victim. Only when they are close enough to pounce do they reveal themselves, and then they will leap and try to slash at their prey. They have a natural shield that can be quickly depleted by shock damage, and when this fails they also lose their ability to cloak until the shield regenerates. Different varieties of stalker attack in different ways - Needle Stalkers prefer to hang back and fling spines from their tails, Spring Stalkers jump in and out of melee range, and Ambush Stalkers tend to pounce into melee and stay there until and unless their shields are depleted. Most Stalkers become far more cautious once their shields are down; they will let out a distinctive roar, and then back off to recharge.
Needle Stalker: Arguably the standard variant of stalker, needle stalkers tend to stay at a distance to fling spikes from their tail at their enemies. If forced into close range, they will claw and bite at their enemy, however these attacks are rather weak. On True Vault Hunter Mode, they are renamed Nitro Stalkers and their spikes deal additional explosive damage. On Ultimate Vault Hunter Mode , they are renamed Clash Stalkers.
Spring Stalker: Spring stalkers are functionally the opposite of needle stalkers, and jump in and out of close combat rather than attacking at range as such, spring stalkers deal far more melee damage than needle stalkers, but have no long-range attack option. If confronted, they will often attempt to move away for another pounce. On True Vault Hunter Mode, they are renamed Poison Stalkers, and their attacks become corrosive. On Ultimate Vault Hunter Mode, they are renamed Pestilent Stalkers.
Ambush Stalker: Ambush stalkers, like spring stalkers, attack at close range rather than use the spikes on their tails. Once within striking distance, ambush stalkers repeatedly assault their enemy until uncloaked. On True Vault Hunter Mode, they are renamed Flash Stalkers. On Ultimate Vault Hunter Mode, they are renamed Blitz Stalkers.
Cyclone Stalker: Cyclone stalkers are named for their ability to spin rapidly while moving towards the target, dealing very heavy damage and deflecting incoming projectiles. Cyclone stalkers are also capable of flinging rotating spikes at enemies, dealing arguably the highest amount of damage of any standard stalker's spikes. On True Vault Hunter Mode, they are renamed Zing Stalkers, and become elementally charged with shock. On Ultimate Vault Hunter Mode, they are renamed Typhoon Stalkers.
Slagged Stalker: A slightly larger variant of needle stalker elementally charged with slag.
Rabid Stalker: Unlike most variants of stalker, rabid stalkers are relentless, biting the target in rapid succession rather than attempting to cloak or fling spikes. This variant is extremely aggressive and has an extremely high amount of health, meaning that it should be made a maximum-priority target if spotted. Rabid Stalkers first appear rarely on True Vault Hunter Mode, and return as a very common foe on Ultimate Vault Hunter Mode.
Tri-Tail Stalker: A variant of needle stalker encountered only in the DLC Captain Scarlett and Her Pirate's Booty. This variant behaves identically to a vanilla needle stalker, but flings a volley of three spikes instead of one at a time.
Chubby Stalker: Chubby stalkers are an incredibly rare variant of badass stalker, which sport far higher health, are much more aggressive and are capable of dealing significantly more damage than any standard variant. As with all chubby enemies, chubby stalkers have a chance to drop one of several Legendary items, such as the Bunny and Bouncing Bonny, and killing a chubby stalker unlocks the achievement/trophy Cute Loot.
Badass Stalker: Badass stalkers behave much like a needle stalker in that they frequently fling spikes. However, badass stalkers have far more powerful shields, significantly higher health and are no strangers to close combat. In True Vault Hunter Mode, they are renamed Super Badass Stalkers. On Ultimate Vault Hunter Mode, they are renamed Ultimate Badass Stalkers.