Freezeflame Fog (5e Trap)
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If a creature moves through a freezeflame fog, it must succeed on a DC 17 Dexterity saving throw or be restrained until the start of its next turn. If the creature is still within the cloud at the start of its next turn, the cloud ignites, dealing 4 (1d8) fire and 4 (1d8) cold damage to each creature within the cloud's area or within 5 feet of it. After the fog ignites, it disappears.