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: 
It's possible the DM is just enjoying a power trip, in which case there's nothing you can do to fix this situation at the *technical level*. As other answers suggest, you need to sit down with your DM and figure out why this is happening at the *social level*.

But that aside...

**Let the DM teleport his monsters away.**

1. You get full XP for these encounters.
2. You got to finish the encounter quicker.
3. This means you get more encounters per session.
4. This means you level faster.
5. This means less risk to your characters!

If your DM isn't awarding the XP, he's ~~being a pain in the~~ not following the rules as written.

If the same nasty monster returns to attack you again, try to Intimidate it into leaving you alone. I think you deserve a check *before it's bloodied* and at least a small bonus to your checks for having defeated the monster before.

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> Intimidate: Standard action in combat or part of a skill challenge.
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> Opposed Check: Intimidate vs. Will
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> Success: You force a bloodied target to surrender, get a target to reveal secrets against its will, or **cow a target into taking some other action.** [DDI](http://www.wizards.com/dndinsider/compendium/skill.aspx?id=14) (emphasis added)
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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.