Permanent Potion of Gaseous Form (5e Equipment)
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When you drink this potion, you gain the effect of the gaseous form spell indefinitely (regardless of concentration). This is generally not considered a good thing. However, there should be a cure, see the Permanent Potions homebrew ruleset for more details. However, effects that prevent spells from being cast stop this effect from working temporarily as long as your are under that effect (after the end of which the form returns at the start of your next turn), and effects that end spells such as dispel magic disable the gaseous form until the end of your next turn.