You have until November 8th to get the Halloween achievements. There are a lot of 24/7 manor event servers so just find one and hunt the horseman every time he shows up.

Don't forget to share your masks to each other if you have dupes.

For those who haven't gotten their share of Portal, act fast!

Portal is free of charge until the 24th of May to celebrate Steam's support of Macs. Visit the game page to get your copy now before its too late!