Enchanted Dust from Warlords of Draenor makes creatures transparent. Currently, on live servers, it works in Mythic+ Dungeons.
When fighting against big bosses, you can use Enchanted Dust to see through them.
The item requires Draenic Dust obtained by disenchanting WoD items and 50 Draenor Enchanting. You can buy it at the Auction House and try it yourself.
Enchanted Dust should be used when you engage the boss because it puts you in combat.