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Fury is a status effect in Mario & Luigi: Bowser's Inside Story that can only be obtained by Bowser when he takes too much damage. While in the Fury status, Bowser flashes red, clenches his fists, and shows a much angrier facial expression with gritted fangs and puffs of smoke spewing overhead. In this state, the damage Bowser deals and takes is doubled, identical to a combination of both POW-Up and DEF-Down. To cure this effect, Bowser can eat a Refreshing Herb, have a set amount of turns pass, or defeat all of the enemies on screen. Choombas go through a similar phase when fired up by Coalbits, making them deal more damage, move faster, and glow red.
In Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey, bosses can gain this status whenever their HP is low enough.