Just before the event can occur, you blast the triggering creature with lightning, forcing it to make a Dexterity saving throw. On a failed saving throw, the target takes 10d8 lightning damage and must make a Constitution saving throw. On a successful Dexterity saving throw, the target takes half damage and no other effects.

If the target fails the Constitution saving throw, the action or effect that triggered this spell is foiled. Any spell slots or abilities that the target would have expended are still expended. Its speed is reduced to 0 feet for the rest of the turn, and if it is the target's turn, the turn ends immediately.

At Higher Levels. When you cast this spell using a spell slot of 9th level, the damage dealt increases by 2d8.