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Arcane is one of the types of damage in Diablo III. It is purple in appearance, and the corpses of monsters that die from Arcane damage glow with a purple light.
During development Critical hits scored with Arcane damage would "silence" enemy targets, preventing mages from casting some spells. This effect was removed along with all other elemental debuffs except for cold during later testing.
Diablo III Damage Types
Damage types will likely change some but are currently Physica], Fire, Lightning, Cold, Poison, Disease, Arcane, and Holy. —Diablo
Whats the difference between poison and disease damage?—WickedBubba
Disease has a damage debuff (both intake and output), and poison has a health debuff (regen/heal). Subject to change of course.—Diablo
Is there much difference between poison and disease? They’re both internal maladies that hurt over a period of time.—Grug