So we killed the Spindleclutch Vamp for Achievment and though, hey lets try the others. After we did Banished and didnt get the achievment...(yep bugged) we went to try Fungal. Well... First:
We werent capable of killing her, best we had was 3%.

Now what we came up so far: (including all "general" infos, for ppl attempting her the first time )

She begins the fight right after you talk to the quest npc (or without a quest: when she is pullsed)

She has 2 signature Abilities and hits quite hard ranged with a spellstaff.

First she will just attack normally and after about 5-10 sec. go into her first ability phase. She will then randomly teleport to 3 different players and leave a black , expanding, damaging area on the floor. So standing all together is a wise idea, cause these area get quite big and do a lot of dmg. The black areas will despawn before she jumps again, but it can actually prevent any melee from actually damaging her! So bring ranged attacks. I call this "teleport phase"

She will then go on with auto attacks and after aprox. 15-20 sec. go into her ability second phase. She will raise her staff and blue flames will spring up around her. Soon afterwards , blue rays will hit each player. These rays can be avoided or cleansed by going into the barrier around the shrine. The rays can deal a massive amount of damage in a very short time (aprox. 3 sec) but the animation can hold longer than the damage effect! The effect can not be blocked and she cant be interrupted. I call this "fire phase"

She will then repeat these phases until the end of the fight.

now since we are talkin about doing it with the achievment, so without cleansing, here are our observations:

1. She sometimes skips the fire phase and immediatly does a second teleport phase: We werent able to determin if thats triggerd or bugged!
2. Fire phase: The damage is very inconsistent. Sometimes its very high (dealing about 3,5 k dmg to an char with 1700 spell res) and sometimes its nothing even worth emntioning. We assume that it has either a random factor, a bug or that its depending on range or damage taken since the last phase or something alike. Nothing consistent was found after 10 trys. (i know, not all too many for secure data...but thats why i am writing here)
3. Sometimes her animation (and aparantly damage) does not apply to single players. It looked like others could block the line of sight when she casts it at first, but we couldnt confirm this. so maybe its just bugged sometimes.
4. We countered her damage with boneshield procs, which worked nice, though we had the feeling, that the dmg she does with her fire phase increases with each time she actually fires it, making it a damage race.

So thats what we came up so far. would love to hear anyone doin the achievment or findin t least the excat mechanic how she works... oh btw we were: melee tank dk vt4, templar vet4 healer, sorc vet 6 spell damage and templar vet4 bow dmg