The WoW Blazing Shadowflame chest is found in the Zaralek Cavern in World of Warcraft, but as it's engulfed in flames, it's not exactly accessible right away. You're greeted with the message "The shadowflame is too strong to bear" when you try to interact with it, and there's nothing nearby that hints at what you need to do.
Unlike the Old Trunk or the Dreamer's Bounty, you will need to go a little further afield to get this chest open. In fact, you'll need to head back several expansions and get your hands on the Onyxia Scale Cloak. With that in mind, here's how to unlock the WoW Blazing Shadowflame chest and where to get the Onyxia Scale Cloak if you don't already have it.
WoW Blazing Shadowflame Chest: How to unlock
The Blazing Shadowflame chest is found on the western edge of Zaralek Cavern, around the large lava pools of Zaqali Caldera. You can see the exact location in the screenshot above. Any effort made to open the chest will be greeted with failure unless you happen to be wearing the Onyxia Scale Cloak.
With the cloak equipped, you can open the chest and loot the Blazing Shadowflame Cinder toy.
How to get the Onyxia Scale Cloak
If you don't have the Onyxia Scale Cloak tucked away in your bank, buying it from the Auction House is the easiest way to get hold of one. The price you pay for it will vary, depending on your server's economy, but if you don't mind forking out the gold, this is by far the quickest and easiest way of acquiring the cloak.
An alternative is to get the leatherworking pattern and craft it yourself, though you'll need a skill of 300 in vanilla leatherworking to get the recipe. Head to Onyxia's Lair in Dustwallow Marsh, defeat the raid boss and loot Onyxia's Head to get the quest "A Most Puzzling Circumstance", then head back to Orgrimmar or Stormwind to hand it in.
The next quest, The Journey Has Just Begun, is only available after you've handed in the previous one and if you have the required skill level in leatherworking. You'll find Overlord Natoj just inside the main gate of Orgrimmar in the Valley of Strength or Major Mattingly just inside the gates of Stormwind City.
The Onyxia Scale Cloak pattern is added automatically, and you should find it when you open up your profession window.