The Grimtotem Weapon

For this quest, you have to get the killing blow on the mob while it is under the debuff from the totem.
This restriction includes hunter pets - I had to put my pet on passive to be sure I got the killing blow and to make this quest bearable.

They did make the cooldown on the totem short and also made the debuff last longer vs. pre-cata, making this a bit less frustrating than before.

Pretty much as others have said. This quest is bugged for characters with pets (namely hunters and warlocks) You should dismiss your pet before attempting this quest, or it will take you forever (something like 1/10 kills before I realised the pet damage was fudging the quest on my warlock)

Once you put your pet away, you'll have no problem.

If you're having trouble with this quest, check the following:

You have to get the killing blow on the crocs. If your pet gets the last hit you will not get credit for the "totem test".
The totem debuff MUST be on the croc at the time of the kill. The debuff lasts for about 6 seconds and reapplies after a split second. It is entirely possible to kill the croc within this split-second and if this happens you will not get credit.

If you are still having trouble make sure you have the right crocs and have the totem down when the kill occurs with the deuff currently on the croc when you get the killing blow.