- Author: Zephan
- Date: December 2, 2021
- Expansion: WoW Classic
In later vanilla patches, there is a stat called “Increases your spell penetration by XX” (also called “Spell Penetration” or “Spell Pen”) which shows up on several Ahn’Qiraj and Naxxramas item pieces. Warlocks already have a way to decrease the magical resistances of their targets with Curse of Shadows, which reduces the Shadow Resistances of your target by 75. However, if the boss you are fighting has more than 75 Shadow Resistance, further Spell Pen is very useful.
For every 1 point of Resistance your target has there’s a 0.25% chance it resists your spellcasts. If it’s a non-binary spell (Shadow Bolt for example) then the average resisted damage is 0,25%, and if it’s a binary spell (Fear for example) there’s instead a 0,25% chance the spell is completely resisted. An item with 10 Spell Pen is therefore worth almost as much as an item with 2,5% hit (assuming your target has any resistances to remove in the first place, otherwise it’s useless).
It’s important to note that when you miss a spell it says “Resist”. If your target would have completely resisted your spell with actual Shadow Resistance it also says “Resist”. So you can’t know for sure if they resisted because you lacked Hit% or Spell Pen.
The amount of resistance on bosses differs. Note that only resistance above 75 matters as that amount can be offset by our curses. There are only 3 bosses that have more than 75 shadow resistance.
For these bosses it is a good idea to use gear with extra Spell Penetration. Warlocks who want to learn even more about how Boss Resistance works can check out this excellent Resist Guide by RoyalGiraffe.