Shiffar's Nexus-Horn

Shiffar's Nexus-Horn is a powerful caster trinket that has a chance to give a buff to spell damage after criting.

Source
Drops from Harbinger Skyriss in the Arcatraz, the 3rd wing of the Tempest Keep on both normal and heroic difficulty.

Effective Damage
The effective +damage granted by this trinket is affected primarily by cast time and critical strike chance. This trinket gains more benefit from shorter cast times and higher critical strike chances.

The formula for calculating the amount of effective +damage granted by Shiffar's Nexus-Horn is -

E = 225 * 10 / (45 + (t / (0.2 * c))) Where... E = effective +damage t = cast time c = critical strike chance

The following Java Program can be used to obtain a table of effective +damage for different casting speeds: public static void main(String[] args) {       float crit; float time; float effective; for(time = 1; time < 6.5f; time += 0.5f) {           for(crit = 10; crit < 101; crit++) {               effective = 225 * 10 / (45 + (time / (0.2f * (crit / 100)))); System.out.println(" " + crit + "  " + time + " " + effective + " "); }       }    }

The four main(Base) casting speeds which should be considered, along with a shortened table for each, are given below:
 * 1.5s - Scorch, Searing Pain, Wrath


 * 2.0s - Lightning Bolt
 * 2.5s - Frostbolt, Shadowbolt, Incinerate
 * 3.0s - Fireball

For comparisons sake, Icon of the Silver Crescent, if used every cooldown, adds 68.7 +damage (25.7 +damage coming from its on-use effect).