How to counter a Tiefling Darkblade?

[Joshua Randall]

Feyslaughter Weapon (level 9+) can nullify teleport powers for a turn.

Dust of Appearance (level 13) prevents him from becoming invisible. And doesn't require an attack roll, which is pretty crazy now that I think about it.

Lots of status effects can render his escape more difficult: daze, immobilize, slow....

 

[Camelot]

If your DM has him escape every time, then there is a story reason for it.

If you find a way to prevent this escape, then the DM will find a way to counter it if it is important to the story.

If your DM wants you to eventually capture the tiefling, then you'll eventually find a way without having to worry about it too much.

If your DM is making you come up with a way to stop the tiefling on your own...then your DM is either really good or really bad.

Anyway, there are plenty of magic items that let you see invisible creatures. It would make sense for your characters to try and plan ahead for your next encounter with the tiefling, so you could try to find one such magic item. I'm sure other EN Worlders know some off the top of their head or their compendiums.

 

[Walking Dad]

The DMG states, that you earn full XP to make the opponent flee... just see the tiefling as your ticket to paragon level