Shadow Focus

From WoWWiki

Shadow Focus
Reduces your target's chance to resist your Shadow spells by X%.
Usable by
Class	Priest
Properties
Location	Shadow, Tier 2
Affects	Shadow spells
Ranks	5
Requirements
Points required	5

Description

Shadow Focus increases your relative spell "level" to an enemy monster, reducing the chance they will resist a portion of, or the entirety of, one of your Shadow spells.

Rank Table

Rank	Amount
1	2%
2	4%
3	6%
4	8%
5	10%

Notes

Many people overlook the power of Shadow Focus, but if you look through your combat log you will notice that although few mobs your own level resist your spells entirely, many of them resist at least some percentage of the damage. Shadow Focus increases your relative spell "level" to the mob, reducing the chance they will resist a portion or the entire spell outright. If you find yourself commonly dealing with mobs several levels higher than you, you will find this talent invaluable. In non-raiding situations, if you are the appropriate level for your zone/instance, 2-3 points should be all you need.

This talent directly effects your chance to hit or miss a mob, which is calculated based on the level difference between you.

 PvE Level    Talent Points Spent / Hit Chance
Difference     0      1     2     3     4     5
------------------------------------------------
    0         96%    98%   99%   99%   99%   99%
    1         95%    97%   99%   99%   99%   99%
    2         94%    96%   98%   99%   99%   99%
    3         83%    85%   87%   89%   91%   93%
    4         72%    74%   76%   78%   80%   82%
    5         61%    63%   65%   67%   69%   71%

 PvP Level    Talent Points Spent / Hit Chance
Difference     0      1     2     3     4     5
------------------------------------------------
    0         96%    98%   99%   99%   99%   99%
    1         95%    97%   99%   99%   99%   99%
    2         94%    96%   98%   99%   99%   99%
    3         87%    89%   91%   93%   95%   97%
    4         80%    82%   84%   86%   88%   90%
    5         73%    75%   77%   79%   81%   83%

If you plan on doing endgame instances/raids as a Shadow priest, 5 points in this talent are required to minimize resists against raid bosses. That leaves a 93% hit chance, so 6% (99% max) must be made up with spell hit gear at 12.6 rating per 1% equals 75.6 rating.

See the articles on spell hit and resistance for more information.