Killer Instinct's combo system is the backbone of performing combos in the game. Outside of the typical "special cancel" system implemented in all fighting games (canceling a normal or a command normal into a special move), the Killer Instinct series has its very own system that allows for longer and more brutal combos.
Killer Instinct combos involve hitting the opponent with a certain special move or an air attack known as an opener, followed by a two hit normal (Light, Medium, or Heavy punches and kickes) known as an auto-double, a special move extending the double known as a linker, and finally a special attack that finishes the combo known as an ender. As the combo continues, the Knockdown Value meter will fill up, and an ender must be used before it fills completely or the combo will be dropped without cashing out. The only way for an opponent to escape from a combo is through a Combo Breaker. In Killer Instinct (2013), normal aerial combos can be performed that do not utilize this system, but can still be broken by Combo Breakers.
An opener can either be an aerial normal, certain command normals, a non-projectile special attack (including its Shadow version), or a Shadow Counter. Some character also have their own unique openers (ex. Glacius' long-distance openers, Thunder's back throw opener). Once an opener hits, a combo can begin. While grounded normal attacks or command normals are not identified as openers, they can be special canceled into openers. Openers cannot be stopped by Combo Breakers.
Recaptures are special kinds of openers that take an opponent who has been launched and brings them back to the ground, "recapturing" them and starting a new combo. Opponents can even be recaptured after the final hit of an Ultra Combo and linked into another Ultra. However, if an opponent is recaptured after an ender, the Knockdown Value will not deplete and the next consecutive combo won't be very long.
After an opener or a linker, a player can input any normal to increase the combo and attack by two hits. A Light auto-double is a quick two hits, a Heavy auto-double is a long two hits and a Medium auto-double is in between. A Combo Breaker can be done at any point in time during the two hits.
Alternatively, a player may also perform a manual instead of a double. Manuals are single hit normals and because of this, it is much harder to Combo Break and the time between the linker and manual can cause a timing based Lockout. However, manuals have a stricter timing window to hit and only causes half the damage (as it's a single hit, not two). Thus this is more of a trap to lure out lockouts and reduce the KV meter than a strictly damage based option.
After an opener or an auto-double, a player can input a grounded special attack (or its Shadow version) to continue extending the combo. Light linkers are a single hit, Medium linkers are two, Heavy linkers are three, and Shadow linkers are usually five. Heavy linkers can only be performed by holding down the button for a Light or Medium linker, as using the Heavy button will activate an ender instead. Combo Breakers can be performed on any of the hits (except Shadow linkers, which require the opponent to hit the breakers in any 3 of the 5 hits) and build KV meter accordingly (except Shadows, which build none).
If a player wants to end a combo and "cash out", a player can input a non-linker special attack (or its Shadow version) or another special attack with the Heavy button. Enders cannot be Combo Broken unless the player goes straight from opener to ender (though if it goes from opener to Shadow ender, it cannot be broken). Every ender has one of four levels depending on the combo produced before the ender shown as a highlighted square under the KV meter - the more highlighted squares there are, the higher the level. All enders will deplete any potential damage on the opponent's health meter and adds additional damage or effects depending on the level of the ender.
There are several types of enders depending on which special move the player ends on. Keep in mind that no character has every single type of ender available, and there is an assortment that characters may possess.
- Damage Ender: Deals a large amount of damage, typically the highest of any available ender.
- ex. Jago's Tiger Fury ender, Sabrewulf's Eclipse ender, Glacius' Puddle Punch ender
- Battery Ender: Builds Shadow Meter depending on the level of the ender, with level four building an entire bar. Some characters’ additionally grant them unique resources, usually also based on ender level. In compensation, they do the lowest amount of damage of any ender.
- ex. Jago's Endokuken ender, Glacius' Shatter ender, Spinal's Searing Skull ender (+ grants skull stock)
- Wall Splat Ender: Pushes the opponent back a fair distance, and if they reach a corner wall, they bounce off of the wall on impact for follow-up attacks or throws.
- ex. Jago's Wind Kick ender, Sabrewulf's Ragged Edge ender, Glacius' Cold Shoulder ender
- Launcher Ender: Launches the opponent into the air. Good for short combos, as an attacker can follow up with an anti-air or a juggle combo.
- ex. Jago's Laser Blade ender, Sabrewulf's Running Uppercut ender, Thunder's Sammamish ender
- Exchange Ender: The same properties as the Launcher Ender, but also causes the attacker and the opponent to switch sides.
- ex. Sadira's Recluse ender, Orchid's Flik Flak ender, TJ Combo's Flying Knee ender
- Hard Knockdown Ender: Knocks the opponent flat on the ground, forcing them to get back up on their own.
- ex. Maya's Tumble Kick ender, Riptor's Tail Flip ender, Aganos' Pulverize ender
- Ground Bounce Ender: Knocks the opponent on the ground hard enough to bounce them back up for a follow-up.
- ex. Glacius' Hail ender, Riptor's Clever Girl ender, Arbiter's Truth Seeker ender
- Auto-Barrage Ender: Unique to TJ Combo. If Combo goes through his entire Auto-Barrage combo using his Combo Trait successfully, he will initiate one of two unique enders - one is a super powerful Damage Ender, and the other is an Advantage Ender that allows Combo to almost instantly open another combo.
- Assault Ender: Unique to Maya. If Maya uses Enmity Strike as an ender, her daggers begin to hover above the opponent’s head and attack every few seconds, with the number of times they attack based on your amount of dagger pips. The daggers’ strikes can’t be blocked, but the daggers can be dispelled if Maya takes damage.
- Burnout Ender: Unique to Cinder. If Cinder uses Fission or Inferno as an ender, the opponent's arms (Fission) or legs (Inferno) are lit on fire. The burning steadily increases the opponent’s potential damage, and if they use an attack that corresponds with where they are on fire (punch attack = arms, kick attack = legs), the flames are fanned and last even longer.
- Upload Ender: Unique to ARIA. If ARIA uses Upload as an ender, she will change Drone bodies during the end of the combo. This is a much safer and faster way of switching Drone bodies without risking the vulnerability time.
- Stagger Ender: Unique to Tusk. If Tusk uses Immortal Spirit as an ender, it will end the combo by inducing stagger on the opponent. Like a wall splat, it can be followed up with other moves, but without the use of a wall.
- Recovery Ender: Unique to Mira. If Mira uses Embrace as an ender, the resulting attack will deal barely any noticeable damage and heal some of Mira's recoverable damage. Amount of recoverable damage healed increases based on ender level.