So I've been thinking about Mahariel's backstory.
HoF and Tamlen find an eluvian, not only intact and working, but active. When an eluvian isn't working, there is no reflection, but Tamlen sees what lies on the other side, he sees some kind of city, probably underground, and there is a great darkness. So he most likely saw a part of the Deep Roads occupied by darkspawn, since there was a bereskarn and later darkspawn in the cave, Mahariel becomes blighted and Tamlen later becomes a ghoul.
But what's interesting is that there was someone on the other side of the eluvian. Someone was watching it, someone somewhat powerful, because it quickly noticed Tamlen, caught his attention and made him unable to look away, then it made some kind of blight burst, which poisoned our HoF, and took Tamlen. At the very least it was a darkspawn emissary. And, well, when Duncan destroyes the eluvian, Tamlen gets trapped on the other side and is forced to find another way out. So I guess there may have been a chance to save Tamlen if we immediately followed him through the eluvian. But oh well, we of course couldn't let more blight to come out of it, we couldn't risk any more lives and we simply didn't know what an eluvian is, we only saw a blighted mirror. But it still hurts.
What also bothers me is that most eluvians, if I remember correctly, lead to the Crossroads. Not all of them, but a lot. So there is a small possibility that our eluvian could've led to the Crossroads. Which is not entirely impossible, because we find the eluvian in a cave that leads to ancient ruins. There we find a statue of one of the Creators (probably Mythal), so the ruins most likely predate the Fall of Arlathan and the Tevinter Imperium rule, so the eluvian wasn't placed here randomly, it's been here this whole time. And it is in the Brecilian forest, very far from the city of Arlathan, so I would assume that an eluvian placed in such great distance from the capital would lead to the Crossroads, from where it'll be easy to get to other places, rather than it would lead dirrectly to a random Deep Roads section. Of course I can be wrong, there could've been other destroyed rooms with a ton of different eluvians (but why though? Ancient elves were clever, wouldn't they rather make one eluvian that leads to the Crossroads instead of a hundred rooms with an eluvian in each of them?). But anyway there is still a chance that Tamlen had been taken by someone to the Fade and then somehow escaped through a way more difficult path than we thought.
