A wee little snafu with the Halloween potions:

We just wanted to let you know that we're aware of the issue with the Halloween potions not working correctly in the Frontiers. The issue is currently being looked into and we hope to have it resolved very soon. We're sorry for the inconvenience everyone. Please keep an eye here for updates!

Updated 1:30am EDT: It took a bit longer then expected but the costume potion issue has now been resolved and you can use them in the frontiers once again. Have a great Halloween weekend everyone!