Battlefield Master

After dozens of BGs and maybe a few hundred hours wasted, I can tell you that Blood of the Enemy Rank 4 is incredibly underwhelming and is 100% not worth the time getting it, even if it's your BiS essence.

You can see the difference between Rank 1 and Rank 4 below:

https://giant.gfycat.com/ImpoliteUnkemptChrysomelid.webm

This achievement is NOT shared account wide, it is character specific.

So you will need to farm 100,000 honor points on a single char to get this, which will unlock the Legendary version of "Blood of the Enemy" (the Azerite essence in BFA).

Try to do at least 1 Alterac Valley every week, it has a weekly quest to Contribute to your Faction's Giant Summoning once, all you need to do is take the Quest, kill a member of the Opposite faction and Remove their Insignia, You're gonna get a random amount of Alterac Items and one of them can be Storm Crystals for the Alliance and Stormpike Soldier's Blood for the Horde, each of these quests rewards you with 1,5K Honor and It counts towards this achievement. in addition to this Quest there's also a Quest to kill the Enemy Leader for another 1.5K Honor, I don't know if that ever resets though.

And here's the Kicker, if your faction is outnumbering the other Faction (Usually the Horde) You can Queue as a member of the Enemy Faction and do their Contribution Quest also, there is no Faction Leader Slaying Quest for the other Faction though, Do keep in mind that this could be considered an Exploit by Blizzard so use it at your Own Risk, I did it once not realizing it works as such

Also, a Daily win for BGs and Epic BGs gives a ton of Honor (nearly 2K) so if you're a PVEer doing this achi, that is a fairly efficient way to Grind Honor

Edit: It seems the Quest to slay the Enemy Leader now gives 150 Conquest & The Quest to Donate is a 1 Time thing