Question: In our gaming group, our storyteller loves to use creatures with teleportation abilities. This is starting to get frustrating since as soon as a creature is bloodied, it teleports away with its next action. We've only managed to kill 1 creature in our last 10 combat encounters.

I'm looking for any powers or magical items that can prevent teleportation.

We do receive full experience for defeating the encounter. The issue is more the frustration of not actually killing the creatures, and that they keep coming back again and again.

Answer: 
Normal teleportation [requires line of sight](https://rpg.stackexchange.com/q/2238/8). So if you can break line of sight from a valid target space, you can prevent teleporation.

Some tactics and methods to accomplish that:

* make them blind.
* tactically use walls (like a `Wall of Fire`) to "box them in".
* immobilize them in a zone like that blocks line of sight (like `Stinking Cloud`).
Aside from any special anti-teleportation powers already mentioned, there's only three things I know of that prevent teleportation:

* A successful save to avoid involuntary teleportation into "hindering terrain".
* The person using the power does not have Line of Sight to either the target object, or the target endpoint, or both.
* The person using the power does not have Line of Effect to the target object.