Chain Lightning

A Sub Trope and combination of Shock and Awe and Herd Hitting Attack, basically an electric attack hits a target, then it jumps towards other nearby targets (may hit allies, depending on the setting).

A Lightning Gun may have this ability. Not to be confused with the song by Steely Dan, or the other song by Rush.

Anime and Manga

 * The Zaguruzemu spell in Gash Bell had this as one of its many effects.

Film

 * In Raiders of the Lost Ark, the Ark is apparently capable of generating an effect that jumps from person to person.

Play By Post Games

 * One of the standard lightning spells in Fate Nuovo Guerra is called this. Genessa (and Zack) is particularly adept at it.

Tabletop Games

 * Dungeons and Dragons: The Chain Lightning spell. After hitting its primary target it arcs to the nearest target (losing 1d6 of damage), doing so again and again until it runs out of energy. The chain lightning spell was modified in 3.0/3.5; this is the first and second edition version. The new version just has secondary targets all taking half damage rather than gradually reducing damage.
 * Warhammer: This is generally how lightning-themed attacks work, for example the Warplightning Cannon. An older edition's Lightning Dragons had a Breath Weapon with this effect. A later edition added a Heavens spell actually called Chain Lightning, it has a chance to jump to a second target after the first, then a third after the second and so on until it fails to jump.
 * In Magic the Gathering, the card Chain Lightning is an interesting example in that the spell's first target (or the target's owner) gets to choose the next target. As long as each player is willing and able to spend red mana on the spell, the process repeats itself.
 * Some more direct examples of Chain Lightning effects would be Cone of Flame (the classic decreasing damage effect), Incremental Growth (a buff-like spell) and Incremental Blight (almost the same as Cone of Flame, but hits creatures only).
 * World of Warcraft card game (and its short-lived miniature game) faithfully recreates the video-game-version's Chain Lightning and Chain Healing spells (the page picture is from the WoW card game, not the MMORPG). This trope is so prevalent in the card game in that many Shamans or Shaman abilities/equipments can cast Chain Lightning, dealing or healing 3 damage to the first target, 2 to the next and 1 to the last.

Toys

 * Bionicle: the Makuta have Chain Lightning abilities, as do the Rahkshi of Chain Lightning that they can spawn. In BIONICLE Heroes for the DS, the fully upgraded Air weapon will do this against multiple enemies.

Video Games

 * The Farseer hero in Warcraft 3 has chain lightning.
 * Several heroes have it in Defense of the Ancients, a Game Mod of War3.
 * World of Warcraft :
 * The Shaman class has chain lightning. After hitting its initial target, it will jump to the nearest enemy, but each jump reduces the damage it does.

Shaman players also have access to a Glyph that causes their Chain Lightning attacks to jump through five targets rather than the usual three, but do 10% less initial damage.
 * Some of the Mobs and bosses invert this with each jump doing more damage to encourage players to spread out.
 * There is also Chain Healing, which functions similar and does exactly what you think it does.
 * Brutal Legend features an axe modification named Chain Lightning that has this effect. The Drowning Doom's Lightning Rod unit has a double-team ability that does this too.
 * All Heroes of Might and Magic games have this. Succubi in the fifth game have a fire variant. It can't hurt other demons, which makes it safe to use
 * Chain Lightning spell in Dragon Age. Any enemy mage with this spell instantly becomes a Demonic Spider. For a few levels at least: it's the only spell whose damage doesn't increase with spellpower, so it rapidly drops off to 'ow that tickles'.
 * Lightning spell in Fable turns into this at higher levels. Nerfed in the sequels.
 * Diablo has a spell that works this way.
 * Diablo II has a few:
 * An ability of the Sorceress.
 * "Proc-ing" items that give X chance to cast X level Chain Lightning upon Attack/Striking/When Struck.
 * Multi-Shot Lightning Enchanted Boss. Thankfully, that quirk of MSLE monsters have been addressed from v1.10 onwards.
 * Some of the pins in The World Ends With You have psychs allow you to make lightning bolts that hit multiple targets.
 * One of the weapons in the Nazi Zombies mode of Call of Duty World at War did this.
 * When you level up Spyro's lightning ability in The Legend Of Spyro, it gains the Chain Lightning ability.
 * Castlevania
 * This was a soul in Castlevania: Dawn of Sorrow.
 * Also featured as one of Charlotte's spells in Castlevania Portrait of Ruin.
 * Resistance Fall of Man has a gun that shoots a bolt of energy that jumps from enemy to enemy, and gets stronger with each body it passes through.
 * Starkiller in The Force Unleashed and its sequel can fry multiple mooks with Force Lightning.
 * Bioshock 2's Electro Bolt 2 plasmid can do this.
 * Numerous weapons in the Ratchet and Clank series have an arcing electricity effect, or can be enhanced with such. The ones that really spring to mind include the Plasma Coil/Plasma Storm (a small electric shot that arcs on impact, and upgrades to fire a bouncing lightning ball that zaps everything in range), any weapon in Deadlocked with the Shock mod, the Shock Ravager/Lightning Ravager (an electricity whip that makes chain lightning in its upgraded form), and the Tesla Spikes/Storm Spikes (tiny lightning rods that arc electricity between each other when you place two or more of them, and also get a chain lightning effect when the weapon upgrades).
 * The Peace Maker in Jak and Daxter's sequels. Fires a small orb of electricity that arcs upon impact and instantly kills nearly every enemy in sight.
 * In Champions Online, this a basic power from the Electricity set. Many/most of the Electricity powers have this chaining-to-another-target as a possible effect actually, but the Chain Lightning power itself can leap every time and to multiple targets if possible. This power is not so great on single enemies, but can bounce back and forth within a small group for some NICE damage by the time it actually finishes.
 * Metroid Prime had a number of "beam combos" which combined a Charged Attack from one of your elemental beams with missiles. The beam combo for the Wave Beam was the Wavebuster, a stroke of lightning which arced between multiple enemies and could be fired continuously.
 * God of War 3: the Nemesis Whip can do this.
 * The Thunder Dancer from Mega Man X 8 functioned like this.
 * In Mega Man ZX Advent, Ashe's secondary shot in Model A form shoots one stream of electricity that arcs between every enemy you lock onto, as opposed to Grey's which fires a homing bullet at each enemy.
 * Kings Bounty has the Lightning spell, which initially only strikes one target.
 * One of Storm's signature powers in X-Men Legends and Marvel Ultimate Alliance.
 * Dungeon Crawl has Chain Lightning spell, which is very powerful.
 * Destroy All Humans: Crypto's Zap-O-Matic can do this after an upgrade or two.
 * In Mabinogi, one of the three basic attack spells is lightning bolt. While at one charge it will only hit one enemy, each additional charge added allows the player to hit one more enemy near it, though it will do less damage each time it jumps. While a player can only charge a spell up to five times, it can work in combination with up to 2 other players' lightning bolts, allowing one to hit up to fifteen monsters.
 * Area of effect shock damage spells on later The Elder Scrolls games do this to hit other targets.
 * Zapper in Purple looks like a joke, until you get at least two enemies of the same type, then it will shoot lightning that connects enemies For Massive Damage.
 * In Star Wars Battlefront II, the primary weapon of the Empire's jetpack-equipped Dark Trooper is a lightning cannon which, to make up for its short range, can charge its shots in order to chain up to two additional nearby targets.
 * The Thunder Laser in Ray Crisis does this, and you can lock onto additional enemies after firing it.
 * Sword of the Stars: The Emitter class of weapons is essentially this as a starship weapon. It's a fairly good backup PD weapon if you don't have (enough) proper PD weapons.
 * The Arc Projector Heavy weapon in Mass Effect 2 has this ability. Irritatingly, it is DLC only.
 * In Mass Effect 3, the Overload ability can be upgraded to this. There's also the "Arc Pistol," a downsized version of the Arc Projector.
 * The 'Overload' ability in Mass Effect 3, can be upgraded to do this.
 * Gizonde in Phantasy Star Online chains to nearby enemies.
 * From In Famous, Cole McGrath's basic lightning can do this after some upgrading, but it's more prominent with Evil Cole's Arc Lightning.
 * Tesla Tanks and Tesla Troopers gains this after promoted to heroic level in Red Alert 2.
 * There's that one electric beam gun thingy in Hellgate London. The beam spreads to nearby enemies, and it can also shock them, so they stop or move slower.
 * Conspicuously absent for the longest time in City of Heroes. By now, it's become a staple of the later-coming Electric powersets (Electric Melee's Chain Induction, Electric Control's Jolting Chain and Synaptic Overload and the Incarnate power Ion Judgment), but is still missing from the earliest one, Electric Blast.
 * The Deus Ex promo for Team Fortress 2 came with the Short Circuit secondary for the Engineer, which fires electricity and hits targets in front of Engineer, AND targets near those, even teammates. In a twist, it's extremely weak (it only does 5 damage), and its main purpose is instead to destroy enemy projectile.
 * Lightning spells in Magicka can hit several nearby enemies at once.
 * There's a skill in Dragon Nest that's named this.
 * The Thunderstrike from Heavy Weapon is this. Upgrading it causes it to hit more enemies and do more damage.
 * In Quake IV, the Lightning Gun does this after being upgraded by a technician.
 * In Age of Wonders, there's a spell called Chain Lightning that does just this, limited to four units attacked in chain and they must be at a certain distance from node to node.
 * Borderlands 2: the new Tesla grenade does this.

Web Comics

 * Order of the Stick: One of the favored attacks of Vaarsuvius.

Western Animation

 * Exo Squad: Maggie Weston's E-Frame has a Chain Lighting gun as its Ace Custom modification.
 * Botanica from Beast Machines has a very powerful chain lightning attack that single-handedly took out a squad of tank drones.