Baleful Blink (EFA - B)

You curse one creature to a frustrating existence on the edge of the Ethereal Plane. Choose a creature you can see within range. The target must make a Constitution saving throw. On a failure, for the duration, whenever it attacks or casts a spell, it flickers between the Ethereal Plane and the plane of existence on which it happens to be.

When it does so, it rolls a d20. On a roll of 11 or higher, it vanishes from its current plane of existence and appears in the Ethereal Plane, its attack misses, or its spell fails. It reappears at the end of its turn in the space it occupied when it flickered. If that space is occupied, it appears in the nearest unoccupied space (chosen at random if more than one space is equally near).