Aegis of Ensnarement allows you to mark targets and trigger a reaction when the marked target attacks others.
Paraphrasing pertinent power text:
If the marked target hits with an attack that doesn't include you, you may use an immediate reaction (after attack is resolved) to teleport the target to any space adjacent to you, after which it grants combat advantage to everyone until the end of your next turn. If no unoccupied adjacent space exists, you can't use this.
It seems like the intent of the power is to grab an enemy who is trying to run amok farther away from you, in which case the text makes perfect sense. But I'm wondering about the (fairly common!) case where the target is already adjacent to you and attacks someone else anyway.
- Can you use the reaction to teleport an already-adjacent target to a separate adjacent space and grant combat advantage?
- Can you use the reaction to teleport an already-adjacent target zero spaces (leaving him where he was) and grant combat advantage?
- If there are no unoccupied adjacent spaces, but the target is already adjacent, could you still do the previous case (teleport zero spaces and grant combat advantage)?