I've been playing through Hell mode on Diablo 3 for the better part of a day and have come across 3 Treasure Goblins. On all the lower difficulties you can either stun or disorientate him to cancel the portal. I've tried doing everything I can to stop him on Hell mode, though, and he still travels through. Is there a way, apart from blowing him up and killing him before he teleports, to stop Treasure Goblins from teleporting away?
For information on Treasure Goblins, take a look at this previously asked question.
From my testing, there is no other way to effectively close the portal besides interrupting the cast and/or destroying the treasure goblin. In Hell mode, all enemies have increased resistance and increased HP. Therefore, you HAVE to output more DPS to prevent him from getting away.
From what I have noticed, once his portal is down, you have a set amount of time to kill him or make him run away from the portal before it doesn't matter: He will get into the portal and your loot is gone.
A few recommendations:
The goblin will open a portal if either of these two occur:
If it's the former, you can cancel the portal; if it's the latter, you can't.