Jailer

A Witch Doctor, Mongrels, and Templar jailed by the Dataminer.

Jailer is a Boss Modifier in Diablo III. Bosses and Champions (and Elites) who possess this ability can "jail" characters and their pets for a short period of time. While jailed an orange circle of light appears around the target, and they are held in that location until the jail dissipates.

Jailer bosses have a 25% chance to jail their targets with each attack, and the effect last for up to 3 seconds, though on Normal difficulty the duration is much shorter than that. Various equipment can also lessen the duration of the effect.

Jailed targets can still fight, hit enemies, cast spells, drink potions, etc. They just cannot move, though some skills will allow an escape from the jail. This boss property is also possessed by a good number of Elites, most notably (and appropriately) by The Warden.

Jailer:

• Monster Level Minimum: 10
• Available to: Bosses and Champions.
  • Uniques: The Warden, Dataminer. Diablo's Bone Prison is not a form of Jailer, but an entirely different ability with a similar effect.
• Damage Type: N/A.
• Additional Resistances: None.
• Will Not Spawn With: Knockback, Nightmarish, or Vortex. (Added in patch v1.0.4.)[1]

Strategy

Jailer is often inconvenient and scary, but as it's only cast occasionally and the duration is fairly short it's not usually lethal. The biggest danger, other than being hit by enemy attacks that you can not move to avoid, comes from other Boss Modifiers. Though Jailer does no damage, it can pair with deadly AoE properties like Arcane Enchanted, Plagued, Desecrator, or Mortar to destroy an immobilized character.

Players need to learn not to panic and to keep fighting while jailed -- new players often freak out and spend all their time struggling to escape, rather than continuing the battle. It's also helpful to know which of your skills can and cannot escape the jail, so you do not waste resources using skills that won't help. For instance, Demon Hunters can not break out with Vault or the backflip from Evasive Fire, though they can cast those skills while jailed, wasting Discipline while moving not an inch, and potentially having no resource left once they are free.

Movement Skills

The jail can be broken out of by a number of movement and defensive skills, while some others do not escape the prison. This section notes all the relevant movement skills and their effectiveness.

Barbarian Skills

• Furious Charge, Leap, and Wrath of the Berserker will break out out Jailer. A Barbarian in WotB form can not be jailed.
• Sprint does not break Jailer.

Demon Hunter Skills

• Smoke Screen breaks the jail when cast.
• Vault and Evasive Fire do not move or break the jail.

Monk Skills

• Serenity grants "immunity to all control-impairing effects" including Jailer. It breaks jails and prevents them from forming.
• Seven Sided Strike escapes the jail.
• Dashing Strike will not break the jailer, but the Monk will teleport to the target, the jail moving with him.
• Thunderclap rune in Fists of Thunder provides a sort of teleport to the first targeted enemy, and can break the jailer effect.
• Tempest Rush does not break out of the jail or make the Monk immune to being jailed.
• All of the Monk's protection abilities also work while jailed, so the class can shield and defend as necessary.

Witch Doctor skills

• Spirit Walk allows the Witch Doctor to pass right through the Jail.
• All pets can be summoned while jailed, and will appear outside the jail and move normally. Pets will be caught in jails if they are active when the jail is cast.

Wizard skills

• Archon will break out of the jail, and a Wizard in Archon form can not be jailed.
• Mirror Image breaks the jail effect.
• Teleport does not break out of jail, but moves the Wizard with the jail remaining around her.

Media

The jailer property does not alter the appearance of the boss or Champion in any way, so players don't know about it unless they see the tooltip hover text, or the orange jail cell pops into existence around them.

• 

  Jailed by a Scavenger.

• 

  Boss with Jailer affix.

The Jailer property is often seen on the random boss attached to the ancient monument event in the Festering Woods.

A Monk and his Enchantress Follower are repeatedly jailed during this Inferno battle with some Blood Clan.