Twilight Oasis is notoriously the most difficult fractal outside of challenge motes in 99 and 100. This is especially true vs. normal T4 groups who are not accustomed to CM/T4/Rec 100 ESS type of LFG group play. What makes Twilight Oasis so difficult for normal T4'ers is mainly the larger groups of mobs that are actually dangerous, and then of course the boss at the end. What makes the mobs & the boss dangerous is that they front mechanics which forces the party to take damage from multiple small sources, a lot of damage that is not so easily avoidable.
The easiest way to make my point here, would be to explain what I have witnessed on the daily reset of 11/27/2018 7:00 pm eastern, to 11/28/2018 7:00 pm eastern. <- It was on that dreadful day that Afflicted/Toxic Trail/Last Laugh fell together in Twilight Oasis. So I had ran in some usual CM/T4/Rec 100 ESS group to completely my own dailies. It was some usual 45 minute job and as we passed through Twilight Oasis, I remember a couple guys mentioning "Afflicted/Toxic Trail/Last Laugh" but I didn't really notice it because it was a strong group and the mistlock instabilities were slightly inconvenient at worst. Later, when I had other friends ask me if I wanted to run T4s with them "these are people who don't CM", I figured sure why not, don't have much else to do anyway. These are people who I've never seen have problems with general T4 runs. When we entered Twilight Oasis with "Afflicted/Toxic Trail/Last Laugh", they began having problems. They had wiped several times on the way to the boss and then eventually called it quits when they were unable to defeat the boss. They tried for something close to an hour to beat Twilight Oasis. I felt bad because usually I could carry these players through a bad situation in a fractal, but not this. I had gone to sleep and woke up, another guy on my contact's list randomly messages me and asks me to help with Twilight Oasis. This is someone I don't normally ever hear from unless he wants help with something difficult. Again, this is a player that I've never seen have problems with any T4 completion. I join this guy's party and they're already at the boss. The team comp is meta minus a BS, so we give it a shot, party wipes at Grenth phase specifically due to how the instabilities interact with the phase. We try multiple times, the party has serious issues with Grenth phase and when they did make it to the final phase, they just couldn't sustain it. The Druid wasn't bad and neither was the mechanical knowledge of the party as a whole, it's just that they weren't an excellent CM ready fractal group. Should they have to be to be able to complete a normal general T4?
So what was making Twilight Oasis so difficult for a general T4 group? Well let's take a look at how these instabilities are interacting with the fractal, which is different than others:
So my direct statement on this issue is that: Due to the special kind of dynamic in Twilight Oasis, which is very different than other fractals, having these 3 mistlock instabilities land together puts Twilight Oasis somewhere between 99 CM and 100 CM in terms of difficulty. It is slightly more difficult than 99 CM and slightly less difficult than 100 CM. These 3 instabilities could land together in any other fractal and it wouldn't increase the difficulty of those fractals by that much, but when it happens in Twilight Oasis, due to the special chemistry that Twilight Oasis mechanics have with these 3 particular instabilities, it is enough of a boost in difficulty to make Twilight Oasis considered a CM.
For the general T4 community and continuity of "how difficult a normal T4 should be", it just might be a great public service to code in that these 3 instabilities never land together ever again in Twilight Oasis.