Bongo (known as Isao in Bare Knuckle Mobile) is the boss of the fourth stage from Streets of Rage and Bare Knuckle Mobile, and in the Mania+ and survival modes of Streets of Rage 4. He is replaced by Big Ben in other games.
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Bongo appears as a large, bald and obese man of Asian descent wearing suspenders. His move set entails only running diagonally across the screen breathing fire. Grappling Bongo is a bad idea - his abundant weight itself passively counters nearly all tosses and slams, causing massive damage (get it?).