Resistance, the flip side
I touched on making your spell hit more dangerous last time. The flipside this time – How do you reduce the danger from other spellcasters? Obviously, Resistance. But, how much, and how useful?
First let’s grasp the core of spell resistance. If the other side casts a spell that has an effect – fear, blackout, invisibility, or anything like that where it either works or it doesn’t – then resistance increases the chance it doesn’t. If the other side casts a damage spell, then it reduces how much damage comes through. If both are possibilities (slows and causes XXX damage over the duration aka Mind Flay), then both effects of resistances are possible. I’m not going into the single roll theory and its application in this post.
According to posts the Guys at Blizzard have made, the best possible resistance is 75%. And through other posts and some serious study, we know how to get that 75%. Easy, actually — have five times as much resistance as the opposing spell-caster’s level. In fact the formula is fairly simple:
([Resistance value]/[spellcaster level * 5]) * 0.75 = Resist Percent.
Let’s take a lower level to show this. 20-29 BG. You’re facing a 29 spellcaster, and you want to know how useful (or not) the +4 shadow resist ring is going to be.
(4 / (29*5) )* 0.75 = 2%.
Of course we can flip that. ([Resist Percent]/0.75) * ([spellcaster level] * 5) = Resist Rating. So, how much resist do we need to get a 1% change against level 70 spellcasters?
(.01/0.75) *350 = 4.6667
Every 4 and 2/3 resistance gives us 1% chance of the level 70 spellcaster’s spell not working (if all or nothing), and/or reduces the damage by 1%. Wheee.
Prayer of shadow protection II – your “Big one” – is 70 resistance. Against a level 70 spellcaster, that’s approximately 15%.
The math works the same for all the resistances. Bottom line – resistance helps, but it’s not everything.