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From Unmariowiki

Bob The Builder is a builder and a person named bob. He appears in the marioverse many times. The first time was in the original Super Mario Bros. and he apeared as a boss. When mario defeated Bowser, Bob The Builder arose from the lava, and mario had to challenge this beast. He is weak to building. He appears again in Paper Luigi, as a boss of fix-it-up castle. His final appearance was in New Super Mario Bros. where mario defeated him. The future looks bleak for bob.