Summon

In Arknights, summons are units that are deployed by certain Operators to help them offensively or defensively.

General

Unless noted otherwise, all summons will be forcibly retreated when the Operator that deploys them leaves the map.

Summon	Operator	Use
"Blazing Sun"		Deals True damage to nearby enemies and Stuns them when deployed. Cannot be summoned at will, instead automatically summoned when Blazing Sun's Obeisance is activated. Not counted towards the Unit Limit but will self-destruct when Blazing Sun's Obeisance expires.
Cursed Doll		Reduces the ATK and DEF of surrounding enemies. Invulnerable and not counted towards the Unit Limit, but will self-destruct after a period of time.
"Freeling"		Attacks deal Arts damage. Cannot be summoned at will, instead summoned through Image Over Form and Finishing Touch. Not counted towards the Unit Limit but will self-destruct after a period of time.
Industrial Water Cannon		Push enemies back in each attack. Invulnerable and not counted towards the Unit Limit, but will self-destruct after a period of time.
Kaminingyo		Behaves identically to Kazemaru's Substitute. Cannot be summoned at will, instead summoned through Origami Art - Twin Shadows. Not counted towards the Unit Limit but will self-destruct when the skill expires.
Ling's Summons		Varies depending on the skill used; see article for details. Up to three (four with Ling's upgraded SUM-Y Operator Module) may be deployed at a time.
Medic Drone		Heals surrounding friendly units. Invulnerable and not counted towards the Unit Limit, but will self-destruct after a period of time.
Mirage		Taunts enemies, has high HP and RES, and can often dodge Physical attacks. Not counted towards the Unit Limit but loses HP over time.
Mobile Buggy Cam		Reveals invisible enemies in the surrounding tiles. Also slightly reduces the speed of nearby enemies with Scene's upgraded SUM-X Operator Module.
Mobile Riot Shield		Taunts enemies and changes Jessica the Liberated's facing to where the M.R. Shield is deployed. Can only be deployed in the adjacent tiles to the Liberated and not counted towards the Unit Limit, but will self-destruct after a period of time.
Mon3tr		Can only be directly healed by Kal'tsit herself and will have 0 DEF if deployed outside her range.
Night Banisher		Applies Silent Sentinel with greater effectiveness to friendly units within its range. Only available for deployment while Overlooking Vision is active. Invulnerable and not counted towards the Unit Limit, but will self-destruct when Overlooking Vision expires.
Phantom in the Mirror		A weaker illusory double of Phantom which shares his skill and has an independent redeployment time than Phantom himself.
Robotter		Reduces the ASPD of blocked enemies.
Rosmontis's Tactical Equipment		Reduces the DEF of blocked enemies and Stuns nearby enemies when deployed. Cannot be summoned at will, instead automatically summoned when "As You Wish" is activated. Not counted towards the Unit Limit but will self-destruct when "As You Wish" expires.
Sandbeast		Extends Ray's range to its own range. Invulnerable and not counted towards the Unit Limit, but will self-destruct after a period of time.
Sand Obelisk		Stuns nearby enemies when deployed. Cannot be summoned at will, instead automatically summoned when Guardian Obelisk is activated. Not counted towards the Unit Limit but will self-destruct when Guardian Obelisk expires.
Skadi's Seaborn		Extends the Corrupting Heart's range. Invulnerable and not counted towards the Unit Limit, but will self-destruct after a period of time.
Soaring Dragon		Varies depending on the skill used; see article for details. Up to three (four with Magallan's upgraded SUM-Y Operator Module) may be deployed at a time.
Tentacle		Nothing special
"Typewriter"		Attacks enemies in a range of up to three tiles straight ahead with lower ATK than Pozëmka but benefits from her skills.

Trap

Traps are deployed automatically by certain Operators and manually deployed by Trapmaster Specialists, in which case they must deployed on tiles without enemies, although Levitating the enemies gives the player a moment to deploy traps beneath them. When a ground enemy (and only ground enemies) is too close to a trap, it will be triggered; note that invisible enemies will not trigger traps.

Trapmasters can notably replenish their trap's count with their skills.

All traps are invulnerable and do not use up the Unit Limit.

Trap	Operator	Use
Champagne Bomb		Deals Physical damage and Slows the victim when triggered, with the former dealt twice if the Bomb has been deployed for at least 3 seconds. Cannot be deployed at will, instead deployed through "Courtesy Gift".
"Clip"		Deals Physical damage when triggered and either Binds or pushes back the victim(s) depending on the skill Robin uses. Up to six/eight (E1)/ten (E2) may be deployed at a time.
Front Toward Enemy		Deals Physical damage and Stuns enemies in the surrounding tiles when triggered. Cannot be deployed at will, instead automatically deployed through Jack in the Box. Will disappear if not triggered after 120 seconds.
Old Day Remnant		Deals Arts damage and drag enemies in the surrounding tiles towards it when triggered. Cannot be deployed at will, instead automatically deployed through Desolate Echoes. Will disappear if not triggered after 30 seconds.
Resonator		Damages enemies when triggered with various additional effects depending on the skill Dorothy uses. Up to six/eight (E1)/ten (E2) may be deployed at a time.
Welcome Mat		Deals Physical damage when triggered and either Stuns or Binds the victim depending on the skill Frost uses. Up to six/eight (E1)/ten (E2) may be deployed at a time.

Reinforcement

Reinforcements are utilized by Tactician Vanguards and can only be deployed on a tile within their attack range, which is designated as a "Tactical Point". When the Tactician attack enemies being blocked by their Reinforcement, the damage they deal is increased.

Should a Reinforcement be KO'd or retreated, it will revive itself over a period of time during which it is invulnerable but can neither attack nor block enemies. Therefore, the Reinforcement can only be relocated by redeploying their respective Tactician.

All Reinforcements cost no DP to deploy and do not use up the Unit Limit.

Reinforcement	Operator	Use
Flowing Shape		Can copy an Operator by placing them on top of the Flowing Shape while its skill is active, giving the Shape most of the Operator's attributes and a trait to either Steal enemy ATK/DEF or create more of itself periodically depending on whether the copied Operator is a melee or ranged one.
Metal Crab Guard Team		Nothing special
Slumberfoot		Can attack Sleeping enemies, which it will target over the others.
Wolfpack		Can have up to 3 Wolf Shadows that is generated over time; each Shadow increases the Wolfpack's block and attacks' hit counts by 1, and is expended to have the Wolfpack survive a lethal attack with fully restored HP.

Support Device

Support Devices are utilized by Artificer Supporters to augment friendly units. An Artificer can only have a limited number of Support Devices deployed at a time.

All Support Devices do not use up the Unit Limit, are invulnerable, and will self-destruct after some time have passed from when they are deployed (except Stainless' Support Devices).

Support Device	Operator	Use
Full Auto Modeler		Buffs the DEF of a melee unit and grants them Shield(s). Up to three may be deployed at a time.
Prototype of Feist's Metal Crab		Given while Stainless uses the Prototype of Feist's Metal Crab skill. Will be attacked by friendly units, who does no damage towards it and attacks enemies over it. Fires a shot that deals AoE Physical damage whenever attacked enough but loses some HP and can be "repaired" by having Artificer Supporters attack it. Also reduces the Physical damage taken by the friendly unit behind it. Up to two may be deployed at a time.
Stainless™ Multifunctional Platform		Given while Stainless uses Extreme Firepower or Efficient Resupply with different effects depending on the skill in question; see article for details. Only one (up to two from Elite 1) may be deployed at a time.
Reliable Battery		Buffs the ATK of a Caster or Supporter (and only Casters/Supporters). Up to two may be deployed at a time.