I was recently discussing interesting tricks that combat casters can use to control the battlefield, and the following scenario comes up.
The party is defending something against advancing enemies. There's a significant area to cover, so they're having to move about. One party member is a melee combat character with access to magic (we were talking about a Duskblade, because our party has one).
- The player readies an action: "when an enemy crosses this line, I will use Dimension Door [or similar] to transport myself to a spot beside them".
- An enemy runs across the line.
- The readied action triggers, and the character appears beside the running enemy.
- The enemy, having not yet finished their move action, keeps running.
- The running enemy exits a square now threatened by the character.
- The player takes an attack of opportunity on the running enemy.
Is this legal?