The best vocation is Elder Druid because of the spell "Exevo gran mas frigo" and the strategy is to cast it as soon as Ferumbras appears.
As Master Sorcer Sudden Death rune is all you have: prepare the rune in crosshairs and hit Ferumbras as soon as he appears. You can select Runic Mastery in your Skill Wheel boost the damage of your Sudden Death Rune.
As Royal Paladin using crossbow and "Exori gran con" boosted on the skill wheel you also have a good opportunity.
Elite Knight is the worst vocation to kill this boss because maybe you won't be able to hit the boss if he spawns away from you, but with luck, if he sapawns right by your side and you use "exeta res" on him you will gain high participation.