Earlier in April in a trailer for shared loot in Borderlands 3, players noticed a shotgun which has the “radiation” damage type. Randy Pitchford, Gearbox CEO, has confirmed on Twitter that slag is being removed in favor of radiation.
In case you forgot, or are completely new to Borderlands, slag was an elemental damage type that didn’t actually do damage, instead, it amplified damage taken from other damage types.
Some players argued that it made Ultimate Vault Hunter Mode (i.e. new game plus-plus) unfun. Enemies had such high resistances and health regen that using slag was a necessity rather than an option.
As it seems, it will have a damage-over-time effect of corrosive weapons and a damage bonus like slag. For now, we wait until April 2020 to see how well it is balanced gameplay wise.