Double or Nothing

You attempt to interrupt a creature in the process of casting a spell. Roll a d20. If the result is an even number, gain the effects of Double; if odd, gain the effects of Nothing.

Double. If the creature is casting a spell of 3rd level or lower, double any damage the spell would deal, or the caster may instead choose a second target for the spell. If it is casting a spell of 4th level or higher, make an ability check using your spellcasting ability. The DC equals 10 + the spell's level. On a failure, this effect doesn't trigger.

Nothing. If the creature is casting a spell of 3rd level or lower, its spell fails and has no effect. If it is casting a spell of 4th level or higher, make an ability check using your spellcasting ability. The DC equals 10 + the spell's level. On a success, the creature's spell fails and has no effect.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, increase the level threshold for the interrupted spell by each level higher of the spell slot you used.