Assume I am playing a druid or warlock with the War Caster feat, which allows me to cast single target spells in place of using a melee attack of opportunity. I also know the thorn whip cantrip. A successful hit with thorn whip can allow me to pull the target 10 feet. I am facing an opponent with the dimension door spell and want to stop them from getting away.
If the enemy spellcaster were leaping or stepping midway through the dimension door, would it be possible to cast thorn whip using the War Caster feat, hit the target and pull them out, thus preventing them from moving with dimension door?
Best Answer
The hostile creature’s movement doesn't provoke an opportunity attack from you, so your War Caster feat isn't triggered.
The War Caster feat (PHB 170) says:
The hostile creature’s movement doesn't provoke an opportunity attack from you, so your War Caster feat isn't triggered.
The Dimension Door spell description (PHB 233) says:
Dimension Door is a teleportation spell, and teleportation doesn't trigger opportunity attacks.
The rules on opportunity attacks (PHB 195) state:
Additionally, spells do what they say they do, and the spell description of Dimension Door does not say it creates a door that you need to pass through; it merely teleports you to the spot within range, so the proposed mechanism to prevent the teleportation from occurring wouldn't work, either.
Thank you to nick012000 for contributing the additional note.