Caustic Bomb

You mold a caustic ball of poisonous gas and acidic fluids between your hands magically compressing it, then you throw the compressed mass at a point in range. Upon landing the mass explodes in a 20 ft. radius sphere centered on that point. Each creature in that area must make a Dexterity saving throw. On a failed save, a creature takes 8d6 Acid damage, has half its movement speed until the end of its next turn, and takes another 4d4 Acid damage at the end of its next turn. On a successful save, a creature takes half damage on the initial and secondary damage application, and does not lose half its movement speed.

A poisonous cloud forms in the 20 ft. radius sphere at the end of your turn that lasts for 5 rounds (roughly 30 seconds) before it dissipates. The round the cloud is formed is counted as the 1st round in the series. A creature that starts or ends its turn in this area must make a Constitution saving throw. On a failed save, a creature takes 3d6 Poison damage and has half its movement speed until the end of its next turn.

The poisonous cloud is flammable. If fire touches the cloud it causes an explosion that reaches 10 ft. beyond the original radius, dealing 6d10 fire damage. Damage is reduced by half the number of dice rounded up at the end of each round that the poisonous cloud is on the field after the round it was created (i.e. 2nd round deals 6d10 during the round, but 3d10 at the end of the 2nd round). If the explosion is triggered, the poisonous cloud is consumed and removed from the field.

At Higher Levels. When you cast this spell using a spell slot of 5th level or higher, the initial damage and poison cloud damage increases by 2d6 for each slot level above 4th.