This spell is rewarded to Enchanters for completing Skylance 3. The other two Skylance missions are not required to get this spell. I got this spell just last night, and I had never done the other two missions.
I don't know the protocol for completing this mission successfully, but I can share a strategy that worked for my group. Most of the group didn't go into the zone at all, at the beginning. I only know that the Bard, who was leading the mission, had some kind of puzzle to solve. (I'm guessing the details of this can be found elsewhere on this site.) So, the Bard went in, accompanied only by the Monk, who basically feigned death the whole time. As the Bard completed one phase of the puzzle, two mobs apparently spawned. Rather than the group fighting them, the Bard simply zoned out where we were waiting, and the Monk (who of course, was in no danger), simply remained FDed, and let the Bard know when the way was clear. Once the puzzle was completed (which probably had us waiting for about 20 minutes), and the mobs cleared, the Monk zoned out. Once together, we buffed and zoned back in, and fought the named mob. I'm guessing the tank had to be especially powerful, since our leader said at the beginning that she doubted we would be able to do this. He did, in fact, die right about the same time the named did. I simply did the Chanter thing. I slowed, tashed, and debuffed the mob, then chain cast my nukes (even though being nuked by an Enchanter is about as effective as being tanked by one).
In spite of her misgivings, we prevailed and I was rewarded this spell.
Now, anxious to test out my new DoT, I went to Torden, Bastion of Thunder, where I farm diamonds for my Jewelcrafting skill ups. And some things I discovered. I was expecting that if the mob had no mana, only the damage aspect of the DoT would function. To my disappointment, I discovered that the spell would not land at all if the mob had no mana. You would simply get the message, "Your target has no mana to effect" before the spell even completed casting, so I switched to my nuke as my charmed mob tanked for me.
I realize, of course, that I don't have thorough information about the mobs or the nature of the quest itself. But I hope this will be a viable strategy for anyone who is attempting to perform Skylance 3 for the reward.
Please note, the chime (whatever it's for) is not rewarded for completing Skylance 3 only. You must do all three and hail the appropriate NPC for the chime. Like I said, I have no idea what the chime is, or why I should want it, but this post is only for the purposes of the spell.
ADDENDUM:
This spell also stacks with Scryer's Trespass.
Edited, Mon Mar 27 14:38:10 2006