MoP has brought ALOT of changes to fear, how it works, most of the changes been under the hood and easily missed, nonetheless incredibly important. I will try to comprise every Fear related change in here, and hopefully come up with some good strats (Correct me if I'm wrong in anything!)
Lets start with the "run-path" of fear, in cataclysm, and hell, for the entire history of WoW when you feared someone he would run off into some random direction (Sometimes towards you.) in Mist of Pandaria Fear consistently makes your enemy run somewhere away from you. This might suck if they are mounted, and your trying to get a long cast of, or when they have some sprint. For better or for worse at least it is consistent >,<
Blood Fear was added to make instant Fear available. Some things of not however. Blood Fear and Fear have the same "cast time" in the sense that Fear's cast time is the equivalent of 1 Global Cooldown, Blood fear has a 10 second cooldown on top of it (so if you chain fear someone he she will have consistently atleast 27 secs of DR on fear) On the other hand it eliminates the possibility of been LOS'ed, Interrupted, etc Consistency is the name of the game with Blood Fear even if it is nominally worse than fear.
Howl of Terror has been reworked extensively. Now it provides the full benefits of an instant fear. That is while in cataclysm it provided only a 6 seconds fear as opposed to an 8 second fear, now it provides the full duration. Added to this, each Direct hit reduces it's cooldown by 1 second. This effect as of now does not have an internal cooldown. I tested it against a rogue and a demo lock. Against both the cool down got reduced consistently to 20 secs. Which means you might need to watch out to howling into a DR in arenas >,<
Now the Succubus, normally considered subpar by most (including me) there was a change that could make this baby come back into the arena. The seduce still DR's with fear, HOWEVER if you take Grimoire of Supremacy and upgrade her into the Shivarra, her mesmerize offer a wide range of advantages. First of it can't be removed by tremor, Beserker rage, Lichborne, nor will of the Forsaken. Secondly it ignores anti-fear effects, meaning a priest will get Mesmerized even if he has Fear Ward (The succubus already did but worth mentioning ), and same for all of the effects mentioned earlier. The shivarra however is not without meaningful drawbacks... Her mesmerize is still channeled, and still shares DR with fear, also it now produces a rainbow effect that screams INTERRUPT ME.
If any of you know of anything I missed, or I got wrong please do tell (Even Grammar >.<)! Thanks for reading, and Good Hunting !