Here is the full list of all 13 Warriors Wrath achievements.
Take down the first Boss
Kill a Centaurian
Kill a Dredmyden
Kill a Sorcerer
Kill a Raven
Take down a Mynaxtor
kill the first chicken
Take down a Crakster
Kill a Ronin
Kill a Dreadgon
Kill a Helligion
Take down the second Boss
Take down the Final Boss