From
http://www.elitegamerslounge.com/home/raidwiki/index.php?title=Terror_in_the_Dark plus a few bits I know.
In The Well request from Mortimer by saying "destroy" and entered saying "know"
The raid takes place in the large eastern cavern of the instance.
Around the room are large blobs of goo, touching them will get you banished into a room with golems and killed.
a tentacle terror x10 are rooted around the cavern and engaged / killed one by one.
Spinning Tentacles[1]: 50,000 DD, knockback. PBAE 100 range cast every 50 seconds
Also every 30 seconds single target fear cast on a few people. If you get feared into one of the goos you get ported.
Very rarely, they may cast Protofission, a PBAE for 25k as well as a hitting you with Sticky Sap, a 7800 DoT, 60 poison counters, snare, melee slow and silence. Range is also 100'.
When terrors reach 50% hp they split into 2x a voracious tentacle terror. Kill them.
Every 2 minutes an add of random type joins:
an acidic ooze, a deadly scorpion, a rust monster, a venomous lightcrawler, a spider swarm (many, mezable)
You have 35 minutes from engage to get all 10 dead.
Have not gotten past that point yet. Had heard something about a fight after that but not sure.