From the Super Mario Wiki
A Trial Stew is an item in Paper Mario: The Thousand-Year Door and Super Paper Mario, made by cooking Couple's Cake with a Poison Shroom. If used, it lowers Mario and his partner to one HP and down to zero FP, but completely fills Star Power.
In Super Paper Mario, the Trial Stew causes the player to lose all but one HP, but increases their point total by an amount equal the amount of HP lost times 100.
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