Here is the full list of all 13 Orc Raid achievements.
Die for the first time
Kill 10 enemies
Kill 100 enemies
Kill 1000 enemies
Kill 7777 enemies
Kill an ice orc
Kill a fire orc
Kill a stone orc
Kill a savage orc
Kill 100 fire orcs
Kill 100 ice orcs
Kill 100 savage orcs
Kill 100 stone orcs