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Rampage (NPC Ability)
From Project 1999 Wiki
NPC will perform an attack round on one extra player other than main tank. Depending on the encounter, you will have to learn how to deal with it. It can go from healing the small damage (Vindicator rampages rarely, for example) to other strategies (Arch Lich rampages every round).
Rampage and Flurry are mutually exclusive with very few exceptions; i.e. if a mob rampages, it won't flurry and vice versa. Enrage is common for many high-level (55+) mobs and even high-level pets.