Slag is an element introduced in Borderlands 2, and is apparently a by-product of the Eridium refinement process. Slag elemental weapons have a chance to coat enemies in slag. Slagged targets take increased damage from all non-slag sources.
Slag damage has no bonuses or penalties against any non-slag elemental target. In Normal Mode and True Vault Hunter Mode, once a target is slagged, any non-slag damage that target suffers is doubled, including effects from elemental affinities, critical hits, melee, and damage over time.
The slag-coating effect lasts 8 seconds on normal enemies. However, many bosses—particularly Raid Bosses—have a special ability which removes Slag effects once every second.
In Ultimate Vault Hunter Mode, Slag effects are boosted to last longer and cause triple damage (+200%) from non-slag sources. Slag on slag damage is also increased by 50%.
After Handsome Jack began researching the properties of Eridium, he also discovered the mutagenic properties of slag, and commissioned an extensive range of tests in the Wildlife Exploitation Preserve. Information given in the mission Doctor's Orders indicates that while many of the tests were conducted on Pandora's wildlife, Jack also ordered the use of human test subjects as well. These would be herded like cattle into the testing facilities where the scientists were forced to experiment on them under duress. The results were often fatal, but at least in the case of Bloodwing there are indications that some test subjects survived the process, but were left in a horribly mutated state.
In The Pre-Sequel, Jack uses slag to power the Eye of Helios by feeding it to the Destroyer's disembodided eye. When Moxxi has Jack's Vault Hunter overload it with slag to engage the failsafe, she actually used it to destroy the Eye after restarting it, thus keeping Jack from using the eye for malicious purposes.
Sources of slag
Though introduced in the mission Rock, Paper, Genocide: Slag Weapons! at around level 8, slag weaponry will not spawn below level 15. The only exception is the mission item given for use in the aforementioned mission, as well as slag-only legendary weapons such as the Slagga which are obtained prior to level 15.
- List of Unique/Legendary/Seraph weapons and items that always deal Slag damage:
- List of Slag elemental skills:
- Purple barrels slag nearby targets when destroyed. They also damage nearby enemies like other barrels, but about half the normal amount, and without a damage-over-time effect.
- Slag weapons have a higher chance (1.5x) to apply elemental effects compared to similar weapons of a different element.
- Almost all in game enemies can be slagged, although some of them, particularly larger bosses, will not change in appearance.
- Slag elemental enemies cannot be slagged.
- Enemies immune to elemental damage over time likewise cannot be slagged. These include crystalisks, constructors, The Leviathan, Jackenstein, Piston's Blimp, Badassasaurus, and Saturn.
- Most raid bosses can be slagged, but have a continuous ability which removes slag effects once per second. It is still possible to cause higher damage while slag effects are active, but the window of opportunity is very small. Affected bosses include Terramorphous, Hyperius, and Voracidous. Pete the Invincible and Master Gee the Invincible are not affected, and can be slagged as normal.
- Slag coating stays on top of any other status effect, allowing for easy identification of slagged targets.
- Spiderants, threshers, and sand worms remove slag effect, along with other damage over time, when they burrow.
- While Krieg's Release the Beast is activated, his extra melee bonus added to a slagged enemy can do damage upwards of 1 million and capable of one hitters on non-badass enemies if a critical hit is achieved
- In real life, Slag is a by-product that is produced when separating metals from ores - it is usually composed of metal oxides and silicon dioxide.