From the Super Mario Wiki
Li'l Boos are smaller Boos that appear in the game Super Mario RPG: Legend of the Seven Stars. They are found in the alternate dimension of Smithy's Factory. Li'l Boos have the same attacks as their weaker counterparts, but have better stats. A Li'l Boo (or a version of one) also appears in Super Mario World 2: Yoshi's Island in the level Bigger Boo's Fortress.
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