Guide: How to get the Warcraft movie transmog items (World of Warcraft)

A total of four transmog items have been released to WoW alongside the Warcraft movie, and luckily they are really easy to get. All you need to do is log in to any character between now and August 1st 2016, and you will be awarded with a Feat of Strength achievement.

Logging in with your first character awards one achievement which gives you two transmog items. To get the remaining two you need to log in to another character of the opposite faction.
Once you've logged into both you will get the achievements on your account, and in Legion the transmogs will be crosscharacter, so it does not matter which characters you get them on. 

The items you get are the following:
Replica Lion's Fang
Replica Lion's Heart

Replica Blood Guard's Cleaver
Replica Staff of Gul'dan

Do I need an active WoW subscription?

No, you do not need to have an active WoW subscription in order to get the achievements, but you do not get the items without them. You can get the achievements from a trail / below level 20 character, and the items will be mailed to you. The problem is that you won't be able to retrieve them from the postbox. But don't worry, once you have the achievement you don't need to worry, and can collect the items once you resubscribe in the future, as long as you login and get the achievements before August 1st 2016.