Its the Crimson rune in Sacrifice. 40% damage boost for 1 minute for every dog sacrificed? Thats awesome! Until you realize that this does not really benefit pet-centric witch doctors as much as it does spell-centric WDs.
120% extra damage is something that a spell caster just cant pass up.. its too good. But having to take these two abilities to make use of it opens up a whole new can of worms.
For one, you are using 1/3 of your ability slots for this. That leaves just 4 ability slots for the stuff that you will actually be using all the time. For a spell casting WD, that means ONE...maybe two damaging abilities.. because you need at least a couple of escapes/CCs to avoid getting mobbed and killed.
The other possibility is that people will begin using the dogs and sacrifice, and then switching out one or more of the skills for something more useful. This is what the "most effective witch doctors" will do..and it will be considered the "proper way to play".. not doing so will be considered incorrect and lazy. Essentially.. it forces you to switch out skills every 60 seconds in order to play your class correctly.. and that isnt fun.
So your choices will be to spam one damage ability over and over with the 120% damage buff. Effective im sure, but not very fun. OR switch out abilities every 60 seconds to take advantage of the buff without sacrificing your flexibility, effective as well, but not very fun.
Personally, id rather they just removed the damage buff from crimson rune completely, and perhaps gave spell casting WDs access to a nice damage buff through a different and more useful ability for them. Perhaps a 100% damage increase against mobs in the Grasp of the dead AOE.