So, two days ago I had the opprotunity to tank while my guild tried Freya for the first time.
It didn't end well.
Freya is what I would call 'slightly hectic'. She begins the fight with a pair of buffs that heal her for 6k HP/sec and increase her healing by 600%, for a total of 42k HP/sec, making her impossible to kill without removing some buffs. Even though she can't be killed like this, she still needs to be tanked, that was the warrior's job.
She also summons a set of adds about every 30 seconds. One of three groups can spawn: a crowd of small lashers, or a trio of two lashers and a water revenant, or one giant ancient. Every time you kill an add, she loses some stacks of the heal-increasing buff. So, the goal is obvious, keep her tanked until enough adds have died, then burn her down.
Simple in theory, very difficult in execution. Many times we'd get a long pause between waves where the DPS were basically idle, only to have two waves spawn within a few seconds of eachother and wipe us.
The mob of lashers wasn't so bad, even before we figured out the trick to killing them quickly they still posed little threat. They have the annoying ability to drop threat, a lot, but they don't hit hard enough to splatter our healers or DPS like an overripe tomato, so that wasn't so bad. They also explode with fire damage when killed, this can be bad if the entire pack dies within a few yards and seconds of eachother. The strategy we eventually adopted was to have everyone stack on Freya when these were out, and drop AoEs, then have everyone scatter when they got to about 30% health, and finish them off like that. It works very well, most of the time we had 10+ seconds left before the next wave of adds.
The trio of two lashers and a water revenant was trickier for my raid. If one dies, it will resurrect at half health 12 seconds later, unless both others die first. So all three basically have to die at the same time. This would be easy, except their health and defenses vary wildly, and the water elemental refuses to stay where I can hit it. In our first 4-5 attempts, one would commonly die way too early, and they would all resurrect, we'd get a second wave and wipe. Since the DPS have to restrain themselves a bit, this phase very commonly ran long even without an early kill and we would get more just when they were about dead. Fortunately, this was easily corrected by shouting "pop EVERY AoE" over vent.
The ancient alone was the simplest of the lot, but when combined with anything else, it would usually get us all killed. You see, he silences the raid. To fix this, everyone has to run under one of the mushrooms growing randomly all over the area. By the time this was done, however, either of the other two phases would have been running amok, and healing would be so badly interrupted that we typically lost someone around now about 50% of the time. This mob is exactly why you don't want another phase running late. It can also stop you killing...
...the trees. They grow all over, one at a time, during the fight. If they aren't killed before too long, they blow up and heal everything for about 40% health. Not a problem if it hits Freya, since she'll be at full anyway, but it can really muck up one of the add packs. We had two hunters tasked to blowing them up whenever they appeared. If we didn't have the hunters, a destro 'lock, or perhaps some kind of mage might have worked as well, as long as whoever it is is ranged and can do about 10k in a matter of seconds with no warning. If for some reason there's no ranged with burst capabilities, I imagine the melee could get creative.
This fight was really, really crazy. I strongly recommend speccing for AoE threat if you're the offtank, and heavy mitigation if you're the maintank. Our guild hasn't yet downed Freya, and with our level of activity, it probably won't even be attempted again for a few weeks.