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