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The steal stat ability is exclusive to the Thief class and to the Super Robot class that Thursday has in Disgaea: Hour of Darkness, its remakes, Disgaea 2: Cursed Memories, and its remakes.

It uses the same mechanics for Stealing items to determine success, so the Thief class is the best.

The formula to determine how many Stats are lost requires clarification. The bonuses may be lost in Transmigration which would not affect Thursday in the first game as he cannot transmigrate in that game.

From Disgaea 3: Absence of Justice onwards, the ability is part of the Heart Steal Evility, allowing anyone that equips it to steal stats.