Your Lightning Bolt, Elemental Blast, Icefury, Lava Burst, and Chain Lightning casts have a 15.0% chance to trigger a second cast on the same target, dealing 85% of normal damage and generating less Maelstrom.
The amount of maelstrom generated by elemental overloads is 75% of the normal amount.
Though not mentioned, the [Lava Beam] ability gained while transformed by the Elemental version of [Ascendance] is affected by this mastery.
Elemental Overload only affects the direct damage done by [Icefury]. It does not affect [Frost Shock] casts under the Icefury buff.
Each ability that can trigger this mastery has a separate spell (typically named <Ability Name Overload>) that's used for overloads. This allows the Shaman to distinguish casted abilities from overload procs in logs.
Trivia[]
This is the first and only mastery to be reintroduced after being removed as one.
Prior to the introduction of masteries, the ability for certain Shaman spells to "overload" has existed in game since Patch 2.0.1 added [Lightning Overload].
Patch changes[]
Patch 9.0.1 (2020-10-13): Now learned at level 10 (was 29). Rank 2 effects are now baseline.
Icefury Overload's damage is reduced by 35% in PvP situations.
Elemental Blast Overload's damage is reduced by 15% in PvP situations.
Hotfix (2016-09-23):Mastery effects increased by 12.5%.
Patch 7.0.3 (2016-07-19): Redesigned as the Elemental Mastery, replacing [Mastery: Molten Earth]. Now learned at level 78 (was 90). Your [Lightning Bolt], Elemental Blast, Icefury, [Chain Lightning], and Lava Burst casts have a 18% chance to trigger a second cast on the same target for 75% of normal damage and Maelstrom generation.
Old: You have a 20% increased chance to multistrike. Your multistrikes deal 35% increased damage. You gain 5% more of the Multistrike stat from all sources.
Patch 6.2.0 (2015-06-23): Now increases multistrike damage by 20% (down from 35%).
Patch 6.0.2 (2014-10-14): Redesigned. No longer the Elemental Mastery, now their secondary stat attunement. Now learned at level 90 (was 80). You have a 20% increased chance to multistrike. Your multistrikes deal 35% increased damage. You gain 5% more of the Multistrike stat from all sources.
Old: Grants a 16% chance for Elemental Overload to occur. Elemental Overload causes a Lightning Bolt, Chain Lightning, or Lava Burst spell you cast to trigger a second, similar spell on the same target at no additional cost that causes 75% of normal damage and no threat. Each point of Mastery increases the chance of Elemental Overload by an additional 2%.
Hotfix (2013-05-23):Elemental Overload version of Lava Burst should now properly deal 75% of the damage dealt by the Lava Burst that activated it.
Patch 4.0.6 (2011-02-08): Procs of Lightning Bolt or Chain Lightning can now generate [Rolling Thunder] charges.
[Echo Chamber]
[Lava Beam] ability gained while transformed by the Elemental version of 
[Ascendance] is affected by this mastery.
[Icefury]. It does not affect 
