A way to cheese the achievements is to form a group with another interested player and go inside Siege of Orgrimmar. You will not need to endure the resurrection timer and you can instantly resurrect yourself. It's still tedious, but not anywhere near as frustrating.
When you put on the costume, you receive a special action button which has a randomized(?) ability. You use the ability on others using the costume to deal damage to them. Once they die, you are credited for the achievements.
-
View User Profile
Posted Oct 31, 2014 (Patch 6.0.3)This achievement is earned by wearing one of the new costumes added in 2014 for the
Day of the Dead.
The costumes you can purchase during
Day of the Dead for this achievement are:
After you complete
To The Afterlife, you open up the achievement 
Vientos! which leads to 
Calavera.
-
View User Profile
Posted Nov 2, 2014 (Patch 6.0.3)A way to cheese the achievements is to form a group with another interested player and go inside
Siege of Orgrimmar. You will not need to endure the resurrection timer and you can instantly resurrect yourself. It's still tedious, but not anywhere near as frustrating.
-
View User Profile
Posted Nov 1, 2014 (Patch 6.0.3)When you put on the costume, you receive a special action button which has a randomized(?) ability. You use the ability on others using the costume to deal damage to them. Once they die, you are credited for the achievements.
Spells you randomly receive are:
-
View User Profile
Posted Nov 1, 2014 (Patch 6.0.3)I've hit other-costumed people 984579408574 times without their health even going down, nor has anyone managed to actually damage me (stun me yes).
-
View User Profile
Posted Nov 1, 2014 (Patch 6.0.3)same here. i keep on dodging the actual damage. with or without armor on
-
View User Profile
Posted Nov 1, 2014 (Patch 6.0.3)The problem seems to be with Dalaran.
I am able to damage and be damaged fine in other cities.