Chain Reaction is a tier 3 skill in Maya's Cataclysm skill tree. It gives each bullet that hits an enemy while Phaselock is active a chance to ricochet to another nearby enemy. The ricochet effect only works with bullets.
Ricochet Chance: +8% per level
Can only be leveled past 5 with Trickster class mods.
Chain Reaction has no additional effect against single targets, but against clusters of foes, and with the right weapons, the result can be an impressive increase in overall DPS.
The chance to ricochet applies separately to each individual bullet. This means that using guns that can fire multiple bullets at a time, such as shotguns, can result in multiple ricochets at once.
Ricochets take full advantage of any gun damage boosts, so skills or items that increase bullet damage - including a user's Amplify Shield - will have the full effect on both the initial hit and the ricochet. This is notable, as it means that using Chain Reaction essentially gives you a chance to double the effectiveness of any gun damage boosts already in effect.
Elemental effects have a chance to proc on each enemy hit, making it possible to cause elemental effects to two enemies with a single shot, or to affect the second enemy even if it doesn't occur on the first.
Weapons that deal splash damage (like some Torgue or Maliwan weapons) also affect both targets, making it possible to deal damage to enemies within close proximity to each other with both the initial shot and the ricochet.
The healing effects of Life Tap can be triggered on both the initial hit and ricochets. Cloud Kill can be triggered on ricochets as well.
When Kinetic Reflection is active, bullets that are reflected back at enemies count as the player's, and thus receive the same chance to ricochet to an additional nearby enemy as normally fired bullets do.
Players do not have to fire at the phaselocked enemy to get a ricochet; any bullet that hits an enemy while an enemy is phaselocked has a chance to ricochet. This allows Maya to phaselock one target and attack a separate cluster of targets in another area, or to phaselock a weak enemy and ricochet off of a stronger enemy who is normally immune to phaselock.
Bullets will not ricochet off of an enemy under the effects of Thoughtlock.
This was caused by a console-only bug that prevented Thoughtlocked enemies from registering as enemies, and thus could not be damaged by allies. The bug was fixed in console patch v1.02.
As of the Commander Lilith DLC, this bug again exists. Chain Reaction will not function in any regard with a target under the effects of Thoughtlock, including ricocheting off of them, or ricocheting towards them.